Structure and Development of Viruses as Observed in the Electron Microscope

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JOURNAL OFVIROLOGY, Dec. 1971, p. 910-918

Copyright ©1971 American SocietyforMicrobiology PrintedVol.in8,U.S.A.No.6

Structure

and

Development

of

Viruses

as

Observed

in

the

Electron Microscope

XI. Entry and

Uncoating

of

Herpes

Simplex

Virus

KANEATSU MIYAMOTO'AND COUNCILMAN MORGAN

Department ofMicrobiology, College of PhysiciansandSurgeons, Columbia University, New York,New York

10032

Receivedforpublication9August 1971

Two morphologically distinct types ofcapsids are described. The dense capsid appearedto bedisrupted nearthe cellular membrane with release ofcorematerial. Thelight capsidwas more stable andwas frequently encounteredclose tothe

nu-cleus, where emptycapsids werealso found.Pretreatment ofcells before infection with either puromycin or actinomycin D markedly decreased the percentage of emptycapsids. It is suggested that thetwo types ofcapsidsplay different roles in theprocess ofinitiatinginfection. One (the dense capsid) releasesdeoxyribonucleic acid(DNA) shortly afterentry.This DNA is transcribed intoavirus-specific

ribo-nucleicacid, which codes foranenzymecapableofalteringthepermeability of the secondtypeofcapsid (thelight capsid). In proximitytothenucleus, the infectious DNA thenescapeswithoutgrossdisruption of the capsid.

Herpes simplex virus has been reported to enter cellsbyfusion of the viral envelope to the cellmembrane with release of thecapsid directly into the cytoplasm (5). In

experiments

with iso-tope-labeled virus,deoxyribonucleic acid (DNA) wasfound to be uncoated in the cytoplasm and transferred to the nucleus (2). Although initial studies showed capsids at stages of dissolution with releaseofcores to the

cytoplasm

(5),

subse-quentinvestigation alsorevealedsignificant num-bers of intact capsids devoid of cores in close proximityto the nucleus.

The purpose of thepresentstudywas to exam-ine indetail the sequentialevents occurring after entryofthe

capsid

intothe cell. In anattemptto clarify the mannerinwhich infection is

initiated,

astatisticalstudyof thedifferentviralformsseen at intervals afterentry was undertaken. In addi-tion, the effects onviral

uncoating

ofpuromycin (inhibitor of protein synthesis), actinomycin D [inhibitor of DNA-dependent ribonucleic acid (RNA)

synthesis],

and ultraviolet (UV) irradia-tion wereobserved.

MATERIALS AND METHODS

Cells and culture media. Monolayer cultures of HeLa cells were maintained in Eagle's minimal essential medium (MEM; Grand Island Biological Co.,GrandIsland,N.Y.) supplementedwith5% calf

serum.

1Postdoctoral Fellowof The DamonRunyonMemorialFund forCancerResearch.

Virus. The Miyama strain of herpessimplex virus

wasused.

Preparation of inocula. The cells wereinfected with

a10-1dilution ofstock virus. Afterincubation for 48 hr, the cells were scraped into MEM and sonically treated for 10 min, and the debris was removed by low-speedcentrifugation. Thevirus-containing super-natant fluid was used immediately.

Virusinfection for time course experiments. Sparse monolayers (5 X 105 cells) in 30-ml plastic flasks (FalconPlastic, Los Angeles, Calif.) werecooled by placing them in an ice bath for 15 min. The cell layers were washed with cold Earle's solution and infected with 0.5 ml of cold fresh virus preparation containing 108 TCIDwo/ml. After placing the flasks on arocker at 4 C for 1hr, the cells were washed with coldEarle'ssolutionand, to synchronize the initiation ofvirus entry, warmedquicklyto37Cbyadding pre-warmed MEM.Theywereincubatedatthis tempera-turefor 0, 2, 5, 10, 20, 30, 40, 60, and 120 minand then cooled to 4 C, fixed for 30 min in situ with cold 1%glutaraldehyde bufferedatpH 7.2, scrapedfrom thesurface of theflask, andpelleted by centrifugation. Metabolic inhibitors. Puromycin dihydrochloride

was obtained from Nutritional Biochemicals Corp., Cleveland, Ohio, and the final concentration was adjusted to 20

pig/ml.

Actinomycin D was kindly supplied by Merck Sharpe and Dohme Research Laboratories, Rahway, N.J., and was used at a final concentration of 5 ,g/ml.

Virus infectionforinhibitorexperiments.After

pre-treatmentwith inhibitors in3ml ofMEMfor different periods at 37 C, cell layers were washed once with prewarmed Earle's solutioncontaining inhibitor and inoculated with 0.5 ml of prewarmed, fresh virus 910

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UNCOATING OF HERPES SIMPLEX VIRUS

(108 TCID5o/ml). The flasks were then placed on a rocker for 1 hr at 37 C. At the end of theincubation period, cell layerswerewashed,scraped, pelleted, and then fixedfor 1 hr with cold 1% glutaraldehyde.

Ultraviolet irradiation. A 5-ml amount of a fresh virus suspension wasplacedin apetriplate(5cm) on anice bath at adistanceof 10 cm from theultraviolet source (GE germicidal 30-w UV light). The virus suspension was agitated frequently throughout the period of irradiation. UV irradiation for 5 and 10 mindecreased theinfectivitytiter from 108TCID5o/ml to 102 and 101TCID50o/ml,respectively.Noinfectivity was detectable when irradiation was prolonged for 30 min.

Isolation of cytoplasmic capsids. Suspensions of fresh virus were concentrated by centrifugation (105,000 X g) and resuspended in Earle's solution. Monolayers of HeLa cells were inoculated with concentrated virus and incubated for 1 hr at 37 C. The cells were then washed with Sorenson's buffer, harvested, frozen, thawed, and subjected to sonic vibration for 10 min. The suspensions werecleared by low-speed centrifugation. Paraformaldehyde at a

final concentration of3% was added to portionsof the supernatant fluid, whichwerekeptat4C for 15 hr, and thensubjectedtoisopycniccentrifugation in CsClasdescribedbySpringandRoizman(9).Bands werecollectedandnegatively stained with 1% phos-photungstic acidfor electronmicroscopy.

Ferritin-conjugated antibody. The 7S antiherpes antibody was kindly provided by B. Hampar (Na-tional Cancer Institute). Rabbits received, over a

period of 8weeks, onecorneal and fiveintravenous injections of the CHR-HSV-3 strain of herpesvirus grown in primaryrabbit kidney (PRK) cells.The7S antibodywasisolatedfrom the serumbygel filtration on Sephadex G-200 (1). Ferritin conjugation was

kindly carried out by K. C. Hsu by a previously described procedure (8).

Application offerritin-conjugatedantibody.Infected cellswerefixed in situwith 1.6%o paraformaldehyde for 5 min, immersed in

10%0

dimethyl sulfoxidefor 30 min, collected by scraping, and pelleted. The pelleted cells were frozen in a CO2-alcohol bath, thawed, resuspended in the ferritin conjugate for 1 hr at room temperature, washed by pelleting and resuspension four times in Sorenson's buffer, and fixedfor 1 hrwith cold 1%glutaraldehyde.

Preparation for electron microscopy. The cell pellets, after fixationinglutaraldehyde, werewashed withSorenson'sbuffer, fixedfor 30 min in1%osmium tetroxide, dehydrated, andembedded in epoxy resin (Epon 812). The sections were stained with uranyl acetate and lead citrate before examination in an RCA 3G or aPhilips200 electron' microscope.

RESULTS

Virusparticles on the cell surface. Twotypes of virionswereobserved atthesurfaceofcellsafter the inoculum was added. Figure 1 was taken 2 minafterwarming the cells to 37 C and illustrates three enveloped particles on the cell surface. In onevirion (marked A), a translucent zone

sepa-ratesthe capsid from the dense core. In the virion marked B, the translucent zone contains finely granular, dense material. (The opacity of this granular material to the electron beam varies

considerably

fromoneviriontoanother.) Forthe sake of simplicity, the former will be termed a lightcapsid andthelatter will be termed a dense capsid. Light capsids constituted 53% and dense capsids constituted 47% of the total particles ob-servedonthecell surfaceatthe end of1 hr at 4C (time 0). Half of the latter exhibited poorly de-fined capsids, as seen inparticle C and as illus-trated at

higher

magnification

in

Fig.

2 and 3.

Virus entry. At time0, no free virus could be found in thecytoplasm.Inthesampleswarmed to 37 C,the site of fusion oftheviral envelope with thecell membranewasoften difficulttofind, sug-gesting that the process occurredrapidly. (Com-pounding the problem is the critical angle and levelatwhich thesectionmustpass throughboth viral envelope and cell membrane toreveal their

continuity.)

Figures 4 and 5 illustrate two characteristic examples offusion, which are believed to consti-tutetheinitialstepof

capsid penetration.

Figures 6and7showlight and dense capsids,

respe'

tively,

just beneath the cell membrane. Theaggregateof dense material at the surface (see arrows) was frequently encountered and presumably either represents remnantsof theviral envelopeor signi-fiesanalteration of the cell membraneatthesite ofentry.Note thatthedense

capsid

(Fig. 7) ap-pears tobelesswelldefined, suggesting thatit is in process ofdissolution. More advanced stages of capsid dissolution are seen in Fig. 8 and 9. Figure 10 shows both types ofcapsids enclosed within a single viral envelope, whereas Fig. 11

illustrates

similar capsids side by side in the cytoplasm close to the cell surface. In the latter example, it is again evident that the dense capsid appears to be disintegrating. Through-out the study, only the dense capsids were seen atvarious stagesof

disruption

in the cytoplasm, an event most commonly encountered 20 min after

warming

the cells to 37 C. Presumably, the core is released soon after the

capsid

enters the cytoplasm, since it was almost always ob-served closetothe cell surface.

Figure12

illustrates

aviralparticlethatlacks a core. Such particles constituted 4 to

7%O

ofany given inoculum. It is hardly surprising that empty capsids gained entry to the cytoplasm (Fig. 13), since theirenvelopes appearedto be no different from thoseof viral particles possessing the dense core, whichispresumed toconsist of nucleopro-tein. Pinocytotic vesicles could be readily distin-guished from such capsids, because the former exhibit aclosely spaced double membrane and the latterdonot.

911

VOL.

8,

1971

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FIG. 1. Thlree characteristictypesofvirions. In thispaper,particleA hasbeenttermed thelight capsid formand particleBthedensecapsid. Asignificacnt proportion ofthe latterexhibitedpoorly defined capsids,asshownl byC.

At2 miii. X 100,000.

FIG.2and 3. Viralparticleswithill-defined capsidsclosetothecellsurface.At 2min. X180,000.

FIG.4and 5. Twoexamples offusionbetweenthecell(totheleft)andtheviralenvelope.At2and5mini, respec-tively. X 180,000.

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~~~~4~~~~~~~4

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FIG. 6. Liglhtcapsidfreeinthecytoplasm.At5 min. X 180,000. FIG. 7. Deniseill-defined capsid.At5 mitt.X 180,000.

FIG. 8 and 9. Capsids undergoinigdissolutionat30anid10min,respectively.X 180,000.

FIG. IO. Lightanddensecapsidswitliinasingle envelopeatthecellsurface.At 10 min. X180,000.

FIG. 1 1. Liglhtand densecapsidsfreewithinith1ecytoplasmclosetothe cellsurface. Thelattercapsidappears to

beinprocessofdissolution. X 180,000.

FIG. 12. Emptycapsidatthe cellsuirface.At2mini. X 180,000.

FIG. 1 3. EmptycapDsidwithinz thecytoplasm.At5 min. X180,000. 913

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MIYAMOTO AND MORGAN

Tenminutes after warmingthecells, light

cap-sids wereencountered in the cytoplasm nearthe

cellsurface, but by 20to 30min the majority had passedtotheperinuclear region and had lost their densecores.In Fig. 14, for example (at 30min),a

light capsid containing a core is visible on the

right about halfwaybetween the cell surface (up-per right corner) and the nuclear membrane

(lower left). Another

capsid,

onthe left in close

proximitytothe nuclear membrane,appearstobe intactbut is devoid ofa core.During theensuing

30min,empty capsidsincreased in number. Two typical empty capsids, each close to a nuclear pore, aremarked byarrowsinFig. 15. With

fer-ritin-conjugated 7S antibody, itwas possible to

demonstrate by specific tagging that such struc-turesareindeed viralcapsids (Fig. 16). Asseenin

this micrograph, occasional capsids inproximity

to the nucleus contained a core, but they were

greatly in the minority.

Theprobablesequenceofeventsleading tothe

empty capsids is shown in the following five

fig-ures. Closeto the surface, after 5 min (Fig. 17), the cores exhibited a density and size that are

characteristic of infectious virus. During migra-tiontothenucleus,mostbecamesmaller (Fig. 18,

20min)and less dense (Fig. 19, 30min).Closeto

thenucleus,althoughafewcapsids still retaineda

fragment of densematerial (Fig. 20, 2 hr, ferritin-tagged), the majority were empty (Fig. 21, 2 hr, ferritin-tagged). Dense intranuclear clumps of granular material frequently were seen in

prox-imitytonuclearpores.Suchstructuresmay repre-sentaggregates ofnucleoprotein thataccumulate

atspecificsites afterreleasefromthe capsids. To ascertain whether changes in thecore

visu-alized by negative staining could be correlated with those observed in thinsections, viruswas

pre-pared as described aboveand examined. Figure

22(A-E) illustrates characteristic virions and shows that all of the gradations from full to empty capsids could readily beseen.

Timecourse of cell-associated virus. To obtain

quantitative data concerning the sequentialevents

associated with viralentry, statisticalcountswere

made of thelocation of viralstructuresinsections of 100 consecutivecells examinedat5,10, 20, 30, 40, 50,60, and 120min after warming thecultures

to 37 C.

Figure 23 shows that the disappearance of enveloped virus at the cell surface was

accom-panied by the accumulationofcapsidsinthe cyto-plasm. Significantly, the number of virions in cytoplasmic vacuoles (pinocytosis) remainedata

relatively low level. It will alsobenoted thatthere

was a discrepancy between disappearance of

ex-tracellular virus and increase inintracytoplasmic

capsids; i.e.,after 10, 20, and 30 min, 52, 44,and 31%,respectively, of the viruslostfromthe sur-face could not be seenin the cytoplasm. Lastly, theprocess ofentryalmostentirelyceasedtoward the end of the first hour, the extracellular virus thenremainingonthe cellular surface.

Figure24 showsthe fate of theintracytoplasmic particlesatsequential intervals afterentry. Dense capsids in the process of disruption were most frequently encountered at early stages before emptycapsidshadbeguntoincrease significantly. The fact that the number of empty capsids was inversely proportional to the number of full cap-sidssuggeststhat thelatterwere derived fromthe former. It should be emphasized that, as stated above, only 4 to 7% of the inoculum contained emptycapsids,whereas by 1 hr65%, and by 2 hr 90%oftheintracytoplasmic capsidswereempty. Effectsofinhibitorsoncapsiddisruptionand the accumulation of empty capsids. Cells were fixed for1 hrafter addition of virusat 37 C and differ-entialcountsin100consecutivecells werecarried outin amanner similar to thatdescribedabove. Puromycin. Pretreatment ofthecells for1 or 2 hr had no effect on viral entry, but there was a marked change in the number as wellas thetype of intracellularcapsids (Fig. 25). The percentage of fullcapsids increased from 50% inthecontrols to

79%O

in cellspretreated with the inhibitorfor 2 hr, whereas the percentage ofemptycapsids fell from

48%o

in the controlsto 4% (2% ofthe cap-sids inthe controls and 17% in the treated cells wereobserved inprocess ofdisruption). Itis evi-dent that puromycin markedly inhibited the loss ofcores from capsids and slowed down capsid dissolution.

Actinomycin D. The effects of the drug were similarto those of

puromycin.

Incells pretreated for2 hrwith actinomycinDbeforeinfection,81% ofviral

capsids

werefullas compared with 48% in the controls, and only9% ofthecapsids were empty as compared with 50% in the controls. When

actinomycin

Dwasadded 10minafter the cells were infected, the percentages of full and empty capsids were similar to those in the con-trols.

UV-irradiated virus. Irradiation of the inoc-ulumfor5mindidnotaltercapsid

entry,

but the percentage offull capsidsatthe end of1 hrrose from 35 (inthe controls) to 70% Irradiationfor 10min

reduced

the number ofintracellular cap-sids

by

30%,

but 97% ofthem contained cores. After 30 min ofirradiation, which

destroyed

all infectivity, no free intracytoplasmic capsidswere encountered, although the rate of

viropexis

re-mained unchanged in comparison with the con-trols.

914 J. VIROL.

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FIG. 14. Full, light capsid halfwaybetween the cell surface(upperright) and the nucleus (lower left). Close to the nuclearmembraneisanemptycapsid.Thecapsidsareindicated by arrows. At 30min.X60,000.

FIG. 15. Twoemptycapsids (marked by arrows) close to pores of the nucleus at the lower left. The hexagonal

shapeof the capsids isevident.At 60min. X 60,000.

FIG. 16. Two emptycapsidsand one containing a core have been tagged with ferritin and are in proximity to the

nucleus, whichoccupiesthe lowerportionofthefield. X100,000.

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916 MIYAMOTO AND MORGAN

J.

VIROL.

1

7

20

FIG. 17-22.

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UNCOATING OF HERPES SIMPLEX VIRUS

DISCUSSION

The presence oftwo distinct types of capsids raises the possibility that theyservedifferent

func-tions in the process ofinitiating infection. Only dense capsids aredisrupted, aneventthatoccurs

v,

250

-Q.

00 150

-_l

0Q

50

Cytoplas,imcCaps,ds 0

-- -Pa,ices -scles

0 10 20 30 40 50 60 120

TIME(minutes,

FIG. 23. Extracellular virions, intracellullar capsids, anid virions within vesiclesat intervals after infectioni. The cells were inoculated with conicentrated virus anid heldat4Cfor Ihrtoallow atiachmenit. The cultures

were warmed rapidly, anid 100 conisecutive cells were

examinledatthe inidicated times.In thisanzd the follow-in2gtwofigures,4to5%G ofcapsidscomprisinigthe iniocu-lumwereempty.

--

-A0-o~~~~~~~~~~~~7

c -,

A

A--_ _-- -Al Dsu, -ri Ca3s

_~~~~~--- _

C 10 20 30 40 50 60 120

TIME(minutes'

FIG. 24. Capsids containzing cores, empty capsids,

antd capsids in process ofdisrutptioti at intervalsafter inzfectioni. The cellsweretreatedasdescribedinFig.23. The timne inidicatesperiodsat 37 C. Onehiundred

conI-secutive cellswereexaminied ineachpreparationi.

9, 200 ._?

° 180

Q.

, 160

Q.)

° 140 \ 120

cu 100

C.)

- 80

2 60

Q.

0

>. 40 ° 20

a)

E

3 FullCapsids

= Empty Capsids

M DisruptingCapsids

Control 1hr 2 hr.

TimeofPretreatment with 20pg/mlofPuromycin

FIG.25. Effect ofputromycin oni capsid disruption anzd loss ofcorematerial. The cellswereexamined1hr

after inoculation of virus at 37 C, durinig which time the treated cells were incubatediin thecontinzued

pres-ence of puromycini. Thepercentages show the relative

n2umbers of capsidsconitainiingcores, capsidsdevoidof

cores,and capsidsinprocessofdisruiptioni.

rapidly and closetothe site ofentry. Presumably, theyare unstable. (Instability ofthedense capsid

is further suggested by the fact that, inanygiven

inoculum,

nearly half of themare poorlydefined

andappeartohave undergone partial disintegra-tion even before entry into the cell.) The light capsids, on the otherhand, are relatively stable,

for theyarerarely disrupted and, during thefirst hour at least, accumulate within the cytoplasm andmigrate toward thenucleus.The progressive

increase in the percentage of empty capsids, as

opposed tothosecontaining acore, suggeststhat thelight capsidsbecomepermeablewithresulting

escape ofthenucleoprotein. Incontrastto adeno-virus, whose core material can actually be

ob-served at stages ofrelease from capsids close to

the nucleus (6), the deoxyribonucleoprotein of herpes simplexvirusappearstobereleasedslowly, rather thanejectedatagivenmoment,anddirect

FIG. 17. Capsidclose to the cell membrane shortly after entry. Thecore islarge, dense, anidsharply defined. At5miin. X 180,000.

FIG. 18. Capsidmidwaybetweeln the cellsuirfaceand thenucleus. Tlhecore issmallbuitstilldenlse.At 20miii.X

180,000.

FIG. 19. Capsidconitainiiigasmall, irregularly shapedcoreoflowdenisity.At 2hr.X 180,000.

FIG. 20. Ferritin-taggedcapsid closetothe nulcleus (attheleft). Afragmenit ofthecore isvisible. At 2 hr. X

180,000.

FIG.21. Thlreeempty capsids closeto the niuclearmembrane (lower portiont ofthefigure). Thecapsidscanl be distiiiguished from the vesicle ofsimilarsize (left third) by thepresenceof specificJerritin label. Qfparticular

inlterest isthepreseiice of ferritiln within thecapsidiiearthe center, suggestingthatthecapsidis ntowpermeable. At 2hr. X 100,000.

FIG. 22. (A-E)Negativelvstainiedpreparatioiisshowing capsidssimilarto thoseenIcounlteredinsectioiis.

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MIYAMOTO AND MORGAN

passage ofaggregated nucleoprotein into the nu-cleus has not been detected. Studies with ferritin-labeledanti-DNAantibodies, which are currently in progress, may help to clarify the manner in whichthe corematerial gainsentry to the nucleus. UV irradiation appears to have sequential effects. Initially the permeability of the capsid or theconfigurationofthenucleoprotein is presum-ably altered so that release of core material is in-hibited or prevented. Further irradiation appar-ently affects the envelope so that attachment occurs but fusion with the cell membrane does notresult.[It is of interest that cellular fusionwas alsoprevented byUVirradiation,anobservation which supports aprevious suggestion (7) that in the case of herpes simplex virus, at least, viral entryandcellfusionmay berelated phenomena.] The effects ofpuromycin and actinomycin D are consistent with the hypothesis that protein synthesis, presumably mediated by viral

entry,

is necessary for the release of nucleoprotein from thelight capsids.

Theforegoing datasuggestthefollowing mech-anisms whereby herpes

simplex

virus initiates infection. After attachment, the viral envelope fuseswith the cellmembrane,permittingegressof capsidsto the cytoplasm. The

capsids

are oftwo distinct types, light and dense. The former are stable and

migrate

toward the nucleus, whereas the latter are unstable and

rapidly disrupt

near the cell surface. Two different interpretations of subsequent events can be proposed. (i) The dense particlesare inertanddonotcontributeto theinfectiousprocess. In this event, DNA inthe light particles codes for a

virus-specific

enzyme, which willultimatelyrenderthecapsid

permeable

to theviral DNA. If such is the case, either the virions contain an as yet undiscovered DNA-dependent RNA

polymerase

similar to the en-zyme found in vaccinia virus

(3,

4)

or a host RNA polymerase is able to reach the enclosed viralDNAandtranscribe it there.

(The

latter pos-sibility seems remote since this reaction would have to occurin the

cytoplasm,

whichis poorin RNApolymerase.)

(ii)

Both

light

anddense par-ticles arerequiredfor the infectious process. The dense

particles,

which are unstable after removal of theviralenvelope,releasetheirDNA nearthe cellsurfacevery

shortly

afterentry. This DNAis

thentranscribedinto a virus-specific RNA, which in turn codes for an enzyme capable of rendering thelightparticles permeable and thereby allowing release ofinfectious DNA in close proximity to the nucleus. It is of interest in thisconnection that Hochberg andBecker (2) reported that only about 40% of the viral DNA becomes deoxyribonu-clease-sensitive inthe presence of puromycin. This probably corresponds to the DNA in the dense cores, which we suggest is uncoated shortly after entry. The remainder of the DNA would remain within the capsid if, in fact, an enzyme must be synthesizedto permit release.

Itistempting to postulate that toinitiate infec-tiontwo types ofparticlesmay benecessary in the case ofcertain other viruses, such as members of the poxvirus group.

ACKNOWLEDGMENTS

This investigation was supported by Public Health Service grantAI-06814from the National Institute ofAllergyand Infec-tious Diseasesand bygrant GB-6013 from theNationalScience Foundation.

LITERATURE CITED

1. Hampar,B.,A. L.Notkins,M.Mage, andM. A. Keehn.1968. Heterogeneity in thepropertiesof7Sand19S rabbit-neutra-lizing antibodiestoherpes simplex virus. J. Immunol. 100: 586-593.

2. Hochberg, E., andY.Becker. 1968. Adsorption, penetration and uncoating ofherpessimplexvirus.J.Gen.Virol. 2:231-241.

3. Kates, J.R.,and B. R.McAuslan. 1967.MessengerRNA syn-thesis bya "coated" viral genome. Proc. Nat. Acad. Sci. U.S.A. 57:314-320.

4. Kates, J. R., and B. R. McAuslan. 1967. Poxvirus DNA-dependent RNA polymrease. Proc. Nat. Acad. Sci. U.S.A.

58:134-141.

5. Morgan, C.,H. M.Rose,and B.Mednis. 1968. Electron micros-copy ofherpes simplex virus.1.Entry.J.Virol. 2:507-516. 6. Morgan,C.,H.S.Rosenkranz,and B.Mednis. 1969. Structure

and development of viruses as observed in the electron microscope. X.Entry anduncoatingof adenovirus.J.Virol. 4:777-796.

7. Nii,S.,C.Morgan,H. M.Rose, andK.C.Hsu.1968.Electron microscopyofherpes simplex virus.IV.Studies with ferritin-conjugated antibodies.J.Virol.2:1172-1184.

8.Rifkind,R.A.,K. C.Hsu,andC.Morgan. 1964. Immuno-chemical staining for electron microscopy. J. Histochem. Cytochem.12:131-136.

9. Spring, S. B., and B. Roizman. 1967. Herpessimplex virus productsinproductiveand abortiveinfection.I.Stabilization with formaldehyde and preliminary analyses by isopycnic centrifugationinCsCI.J. Virol.1:294-301.

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Figure

FIG..^S-particleAttively. 2FIG. 1.Thlree characteristic types of virions. In this paper, particle A has beent termed the light capsid form and B the dense capsid
FIG..^S-particleAttively. 2FIG. 1.Thlree characteristic types of virions. In this paper, particle A has beent termed the light capsid form and B the dense capsid p.3
FIG. 6. Liglht capsidfree in the cytoplasm. At 5 min. X 180,000.FIG. 7. Denise ill-defined capsid
FIG. 6. Liglht capsidfree in the cytoplasm. At 5 min. X 180,000.FIG. 7. Denise ill-defined capsid p.4
FIG. 15.shapeFIG. Two empty capsids (marked by arrows) of the capsids is evident. At 60 min
FIG. 15.shapeFIG. Two empty capsids (marked by arrows) of the capsids is evident. At 60 min p.6
FIG. 17-22.
FIG. 17-22. p.7
FIG. 25.afteranzdcores,encethen2umbers Effect of putromycinoni capsid disruption loss of core material
FIG. 25.afteranzdcores,encethen2umbers Effect of putromycinoni capsid disruption loss of core material p.8
FIG. 23.anidexaminledlumin2gheldwereThe Extracellular virions, intracellullar capsids, virions within vesicles at intervals after infectioni
FIG. 23.anidexaminledlumin2gheldwereThe Extracellular virions, intracellullar capsids, virions within vesicles at intervals after infectioni p.8
FIG. 24.antdinzfectioni.secutiveTheCapsidscontainzingcores,emptycapsids, capsids in process of disrutptiotiat intervals after The cells were treated as described in Fig
FIG. 24.antdinzfectioni.secutiveTheCapsidscontainzingcores,emptycapsids, capsids in process of disrutptiotiat intervals after The cells were treated as described in Fig p.8

References