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Evidence for recombination between N- and B-tropic murine leukemia viruses: analysis of three virion proteins by sodium dodecyl sulfate-polyacrylamide gel electrophoresis.

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Copyright©1977 AmericanSocietyforMicrobiology Printed inU.S.A.

Evidence

for Recombination Between N- and

B-Tropic

Murine

Leukemia

Viruses:

Analysis

of Three Virion

Proteins

by Sodium

Dodecyl

Sulfate-Polyacrylamide

Gel

Electrophoresis

JOHNSCHINDLER, RICHARD HYNES,ANDNANCYHOPKINS*

Center for CancerResearch, Massachusetts Institute ofTechnology, Cambridge,Massachusetts 02139 Receivedfor publication 29March 1977

We have used sodium dodecyl sulfate-polyacrylamide gel electrophoresis to

analyze thevirionproteinsofanN-andaB-tropicC-typevirusderived from the

BALB/c mouse and 21 putative recombinants, designated XLP-N viruses,

ob-tained fromsevencrossesbetweenthese N- andB-tropic viruses. All the XLP-N

viruses are N-tropic but possess the XC plaque morphology of their B-tropic

virusparent. Threevirionproteins, p15,p30, and gp7O, of the parental viruses

each differ in electrophoretic mobility. Two recombinants were found that

possess a p15 that comigrates with p15 of the B virus; 19 possess ap15 that

comigrateswith N virusp15. Sixteen recombinantspossess agp7Othatmigrates

like thegp70oftheBvirus;fourhavegp70withanelectrophoreticmobilitylike

that ofthe N virusgp7O. All21recombinantspossess ap30 thatcomigrates with

p30 of theirN virus parent. Given the originandphenotype ofXLP-N viruses,

these results wouldseem toprovidegood evidence that these virusesare

recom-binants.

Naturally occurringecotropic murine

leuke-miavirusescanbe classified accordingtotheir

host range as either N-tropic or B-tropic

de-pendinguponwhethertheygrowpreferentially

oncells derived from NIH Swiss mice (N-type)

or BALB/c mice (B-type), respectively (8).

Inbredstrainsofmice canbeclassifiedaseither

N-orB-type, and thisphenotype is determined

byagenecalledFv-1 (22,23;reviewedin

refer-ence 19). Restriction toward a virus of the

"wrong" tropism is inherited as a dominant

trait. The restriction of viral growthon acellof

incompatible Fv-1 type is relative rather than

absolute and occurs after virus absorption and

penetration but before integration of proviral

DNA (13, 16, 17, 27).The viraldeterminants of

N- or B-tropism have not yet been identified

(11,24). The Fv-1 gene plays a role in

determin-ingsusceptibilitytoleukemogenesis by N- or

B-tropicmurineleukemiaviruses presumablyby

retarding the spreadandresulting viremiaofa

virus ofthe wrong tropism (see 19).

Using plaque morphology (9, 25) and N- and

B-tropism as genetic markers, Hopkins et al.

(12) havepresented biological evidence for

re-combination between an N-tropic virus that

makes smallXC-plaques (SP-N) and a B-tropic virus that makes large plaques (LP-B), both

derived fromthe BALB/c mouse: after

coinfec-tionwith SP-N andLP-Bthey obtainedviruses,

called XLP-N, thatareN-tropic butmakelarge

XC plaques. Hopkins etal. (10) have also

ob-tained evidence based on antigenicity, that

XLP-N viruses arerecombinants. We were

in-terested inextending this biochemical analysis,

since analysis of a number of recombinants

mightproveusefulinidentifying and mapping

the viral determinants of XC plaque

morphol-ogy and N- and B-tropism. Famulari,

O'Donnell,and Fleissner(personal

communica-tion;see 11)have shown that three virion

pro-teins of some N- and B-tropic virus isolates

derived fromBALB/c micecanbe distinguished

by their mobility on sodium dodecyl sulfate

(SDS)-polyacrylamide gels. These are p15, an

internal virion protein, p30, the major

struc-turalprotein of the capsid of thecoreshell,and

gp7O, the majorenvelopeglycoprotein which is

responsible forspecificabsorption of C-type

vi-ruses tocells. O'DonnellandStockert(20)have

shown that these viruses also differ in their

abilitytoinduce

G1Q,

anantigenicdeterminant

believedto resideongp7O (28). These

observa-tionsprovideduswith ameans ofaskingifthe putativerecombinants obtainedby Hopkinset al. (12) possessed p15, p30, and gp7O proteins

withtheelectrophoreticmobilitycharacteristic

oftheir N- or B-tropic virus parent. Here we

present the results ofSDS-polyacrylamide gel electrophoresis analysis of virion proteins of 21 XLP-N viruses obtained from seven independ-ent crosses between SP-N and LP-B viruses.

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VIRION PROTEINS OF N- AND B-TROPIC VIRUSES

Analysis of these viruses for the ability to in-duce the Gx antigen has been reported previ-ously (10).

MATERIALS AND METHODS

Cells, viruses, and media. Sc-1 cells (7) were grown in Dulbecco modified Eagle medium with 10%inactivated fetal calf serum and antibiotics. The origin ofSP-N (9), LP-B (B-clone-18) (15), and XLP-N viruses (12) has been described. XLP-N viruses werepurified either by plaque purification (12) or by themicrotiter method (26).

Virus purification and gel electrophoresis. The preparation of virion proteins for gel electrophoresis has been described (11). Briefly, virus was purified by bandinginsucrose gradients and thenpelleted. Electrophoresis of virion proteins was on Laemmli (18)slab gels asdescribed (11). Immunoprecipitation of the p15 virion protein was performed with goat anti-AKRp15serumusingNonidet P-40-solubilized virus followed by precipitation with pig anti-goat immunoglobulin G. The antibodies were a gift from Nancy Famulari.

RESULTS

Parental viruses SP-N and LP-B possess p15's, p30's, and gp7O's that each differ in

electrophoretic mobility on

SDS-polyacryl-amide gels. Virus was purified from culture

fluids of Sc-1 cells (a cell line that does not

exhibit Fv-1 gene restriction) infected with either SP-N or LP-B virus and disrupted with

SDS, and the proteins were separated by gel

electrophoresis. Figure 1 shows a slab gel on

which thevirion proteins ofSP-N and LP-B are

visualizedbyCoomassie brilliant blue staining.

The identificationofp30 isbased onpublished

data (1) and on a comparison with molecular

weight markers (Fig. 1,track1). The

identifica-tion ofthe p15 band isbased on unpublished

observations ofN. Famulari and E. Fleissner

(personal communication), on published data

(1, 14), on acomparison with molecular weight

markers, andonthe factthatthis bandcan be

precipitated using antiserum specific for p15

(unpublished data).It canbeseen inFig.1that

thep15andp30proteinsof SP-NandLP-Beach

differinelectrophoretic mobility: the p30 of

SP-N runsslightly ahead of p30 ofLP-B whereas the N virus p15 migrates slightly behind the

p15 ofLP-B. These differences were observed

not only on the standard Laemmli gel system (18), but also on phosphate-buffered SDS gels

(6), 6 M ureaphosphate-buffered SDSgels,6M

urea Laemmli gels, and low-bis Laemmli gels

(5) (unpublisheddata).

gp7O was visualized by autoradiography of

gels containing virion proteins labeled with 14C-aminoacids(Fig. 2). Thegp70wasidentifiedby

comparison with molecular weight markers andbythe fact that thisband could be labeled

-p30

A:,;.::

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~.

.

....

1

2

3

4

5

FIG. 1. Comparison ofp30 and p15 virion pro-teinsofparentalvirusesSP-N and LP-B.Figure1 is an 8to 24%slabgelstained with Coomassie brilliant blue. Samplesare asfollows: 1, Markermix:

phos-phorylase A, 90,000 daltons; catalase, 62,000 dal-tons;creatinekinase, 40,000daltons; carbonic anhy-drase, 29,000 daltons; cytochrome c, 12,700daltons; 2and 4, SP-N;3and 5, LP-B.

with[14C]glucosamine (unpublished data).The

gp7O of SP-N migratesahead of thegp7Oof

LP-B. The differences in electrophoretic mobility

betweenthep30's andthep15'sof SP-N and

LP-Bcan also be seenontheautoradiograminFig.

2, but the difference isnotas clearas inFig. 1

since the exposure time necessary to detect

gp70results in overexposure of thep15andp30

bands.

Virion proteins of recombinants between SP-N and LP-B. Having determinedthat the

pi5, p30, and gp70 proteins ofSP-N and LP-B,

theparentalvirusesusedtogenerate the

puta-tive recombinants, could be distinguished as

701

VOL. 23, 1977

.", --

N

...B

--.

w

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702 SCHINDLER, HYNES, AND HOPKINS

"O*

CIO

_- w

B

N

B N

_"_"

a_

Id~

ing p30 bands. Thisgel shows the p30's ofsix

recombinants, and, for comparison, each is

flanked by the parentalviruses SP-N and

LP-B.All of therecombinants shownpossess ap30 thatcomigrateswith thep30 of SP-N.Figure5a

and b shows gelsonwhichvirionproteinswere

loadedat a concentrationoptimal for

visualiz-ingp15 bands. Of the recombinantsshown,two

(Fig. 5a, track9, andFig. 5b, tracks 2 and4)

possess a p15 that migrateslike thep15of

LP-B.

Figure 6 is an autoradiogram showing the gp7O's of six recombinants. Five of these

recom-_0 D

70

binants possess a

gp7O

that

migrates

like the

gp7O of LP-B; one (track 4) possesses a gp7O

whose electrophoretic mobility is like that of

SP-N gp7O. Some variation in the width ofgp7O

bands has beennoted, and sometimes the result

of this variationis to give the impression that

recombinant virus gp70's differ slightly from

those ofeither SP-N or LP-B; however, wedo

notknow ifthisdifference issignificant.

Table1is a summaryofdata from thistype of

analysis ofall 21 recombinants. Of the 21

vi-- p30 ruses, 16possess agp7O thatmigrateslike the

gp7O ofLP-Band2 outof21possess ap15that

comigrates with p15 of LP-B, whereas none

possesses a p30 that migrates with the p30 of

LP-B. All ofthe remaining proteins (with the

exceptionof thegp7O of recombinant5-1,whose

40

-0

-NW4NO

-

p15

1

2

3

4

FIG. 2. Comparison of gp7O protein of SP-N and LP-B viruses. Autoradiogram of '4C-labeled virion proteins; 8to20%slab gel. Samplesare asfollows:1 and3, LP-B;2and4,SP-N.

predicted,wecouldnowaskwhetherclonal

iso-lates of XLP-N virus possessed p15, p30, and gp7Oproteins with theelectrophoretic mobility characteristic of the corresponding proteins of their N-orB-tropic virusparent.Sc-1 cellswere

infected with each of21clonal isolates of XLP-N derived from seven independent crosses of

SP-N and LP-B. Much of the information

per-tainingto theorigin ofthese viruses has been reported (10, 12). It is summarized in Fig. 3.

Figure 4isagel onwhich virion proteinswere

loaded at aconcentrationoptimal for

visualiz-CoinfectSc-i cells (8) withSP-N andLP-B viruses

J,

Use progeny'toinfect

NIH/3T3cells

Harvest progeny2 3 days later. Infect NI /3T3 cells

Harvest progeny3 3 days later. Determine end point titer by in-fection of

NIH/3T3 cells

Harvestprogeny4from end point infection. Cross (1)Plaque purify XLP-N from progeny4 to

obtain 1-Pl.

(2) Microtiter clone XLP-N fromprogeny3to obtain2-1, 2-2.

(3) MicrotitercloneXLP-Nfromprogeny3to obtain3-1, 3-2.

(4) Microtiter clone XLP-N fromprogeny3to obtain4-1.

(5)Microtiterclone XLP-N fromprogreny3to obtain5-1, 5-2, 5-3, 5-4, 5-5.

(6)MicrotitercloneXLP-N fromprogeny3to obtain6-1, 6-2, 6-3.

[image:3.503.68.256.78.481.2]

(7)Plaque purify XLP-N from progeny' to obtain 7-Pl, 7-P2, 7-P3, 7-P4, 7-P5, 7-P6, 7-P7.

FIG. 3. Origin of XLP-Nviruses.

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VIRION PROTEINS OF N- AND B-TROPIC VIRUSES 703

B

R

N

R

B

R

N

R

B

R

N

R

- - - -_- .

--

-p30

1

2

3

4

5

6

7

8

9

10

11

12

FIG. 4. Comparison ofp30protein of SP-N, LP-B, andrecombinants. An 8 to 24% slab gel stained with Coomassie brilliant blue. Samples are as follows: 1, LP-B; 2, 2-1; 3, SP-N; 4, 2-2; 5, LP-B; 6,1-PJ;7, SP-N; 8, 4-1; 9, LP-B; 10, 7-P2; 11, SP-N; 12,5-4.

electrophoretic mobility has not been

deter-mined)appear to migratewith those ofSP-N.

The last column in the table shows the

re-sults ofanalysis ofthe parental and

recombi-nant viruses for the ability to induce the

G1x

antigen, an antigenic determinant believedto

reside on the gp7O ofsome murine leukemia

viruses and that is present oncells infectedby

the N-tropic (G+) but not the B-tropic (G- )

parent of the recombinants. These data are

taken fromHopkinsetal. (10). XLP-Nviruses

that are G& possess a gp7O that appears to migrate with SP-N virus gp7O, whereas the

gp7O of G1x XLP-N viruses migrates like the

gp7O of LP-B virus. This result is consistent

with evidence suggesting that

Gjx

resides on

gp70 (28).

DISCUSSION

We have used SDS-polyacrylamide gel

elec-trophoresis toexaminethree virionproteins of

SP-N, an N-tropic virusthat makes small XC

plaques, LP-B, a B-tropic virus that makes

large XC plaques, and 21 large XC

plaque-forming N-tropic recombinants, designated

XLP-N viruses, betweenSP-N andLP-B. That

XLP-N viruses are recombinants was

sug-gested from their biological properties (12)and

from antigenic analysis (10). Since Famulari

and Fleissner (personal communication) had

shown, and we have confirmed here, that the

p15, p30, andgp7O proteins ofN- and B-tropic viruses of BALB/ceachdifferinelectrophoretic

mobility on SDS-polyacrylamide gels, we

ex-amined theseproteins in XLP-N viruses to

de-termine whether the recombinants inherited

both SP-N- and LP-B-like proteins. We have

found that some XLP-N viruses possess ap15

and/or gp70 with the electrophoretic mobility

characteristic of the corresponding proteins of

their B-tropicvirus parent.

A simple interpretation of these results is that XLP-N viruses that possessap15orgp7O

that comigrates withp15orgp7Oof LP-B inher-ited the corresponding genes from LP-B and,

similarly, that migration of an XLP-N virus

p15, p30, or gp70 with the corresponding pro-teins ofSP-Nimplies inheritance of the

corre-spondinggenes fromSP-N. However, sincep15

and p30 are cleaved from a precursor protein

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C

M

m

B

R

N

R

B

R

N

R

B

-~~~~~~~4--__~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~,.f

4

5

6

7

8

D

B

R

B

R

B

R

B

-_w_

...AIN..WI

_^0

a_

a

_a

a

.

0

DI

q _ | -I

2

3

4

5

6

FIG. 5. Comparisonofp15proteinofSP-N, LP-B,and recombinants.An 8 to24%slabgelstained with Coomassiebrilliant blue.Samplesareasfollows:Gela-1,marker mixasinFig. 1; 2,LP-B;3,5-2;4, SP-N; 5, 5-3; 6,LP-B; 7,5-4;8, SP-N; 9,5-5; 10, LP-B. Forgel b:1, LP-B (the band belowp30 inLP-B is a

contaminatingcellproteinpresent inthisparticular preparationof virus); 2, 5-5; 3,LP-B;4, 6-2; 5,LP-B; 6,

6-3; 7, LP-B.

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VIRION PROTEINS OF N- AND B-TROPIC VIRUSES 705

. , , . ., o_ *f .

B

R

N

R

B

R

N

o a

e e e S

S

do

1 234 5

N

R

B

RN

B

S .4

"-

<i

o

e

a

- a

-gp7O

-p30

-p15

[image:6.503.49.447.79.438.2]

6

7

8

9

10

11

12

13

14

FIG. 6. Comparison of thegp7O protein of SP-N, LP-B, and recombinants. Autoradiogram of'4C-labeled

virionproteins;8to 20%slab gel.Samples are as follows: 1, LP-B; 2,1-PZ;3,SP-N; 4, 5-4; 5, LP-B; 6, 7-6; 7, SP-N; 8, SP-N; 9, 6-1; 10, LP-B; 11, 3-2; 12, SP-N; 13, 6-3; 14, LP-B.

codedforbytheso-called gag gene (23, 29), and

since the "rules" governing this cleavage are

not known, otherinterpretations can be

imag-ined, and studies on the primary structure of

the proteins involved would be necessary to

confirm thissimple interpretation.Inany case,

that XLP-N viruses inherit proteins with the

electrophoretic mobility characteristic of the

corresponding proteins of LP-B virus would

seem to provide evidence that these viruses

have inherited portions of the LP-B virus

ge-nomethat determine the molecular parameters

of those proteins. Thus, the results presented

provide evidence that XLP-N viruses are

ge-neticrecombinants.

Of the 21recombinants studied, 16possess a

gp7O that comigrates with the gp70 ofLP-B.

Only2of the21recombinantspossessap15that

comigrates with the p15 of LP-B, and none

possessesap30 withtheelectrophoretic

mobil-ityof LP-B p30. Recombinants obtained from

any one crosscould have arisen from asingle recombination event, unless they have been

shown to differ in their virionproteins. Thus,

theminimumnumber ofindependent

recombi-nantsstudied is 11, ofwhich7have a gp7O with

the electrophoretic mobility characteristic of

LP-B virus gp7O and 2 have a p15 that

comi-grateswithp15 ofLP-B.

Ifone makes the assumption that

comigra-tionofXLP-N virusproteinswiththoseofSP-N

or LP-B implies inheritance of the

corre-sponding gene from the N- or B-tropic parent,

ifone assumes that recombination is equally

probable along the genome, and if one also

assumesthat theonlyselection pressures

oper-

---VOL. 23, 1977

Om

ilp -4

Owe am* one

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706 SCHINDLER, HYNES, AND HOPKINS

TABLE 1. Results of analysis of three virion proteins of parental and recombinant viruses by

SDS-polyacrylamidegelelectrophoresis

Electrophoretic mobility of:

Virus p15 p30 gp7O G,,a

SP-N Slowerb Faster Faster +

LP-B Faster Slower Slower

1-P1 Like N Like N Like B

2-1 N N N +

2-2 N N B

-3-1 N N B

-3-2 N N B

-4-1 N N N +

5-1 N N -c +

5-2 N N B

-5-3 N N B

-5-4 N N N +

5-5 B N B

-6-1 N N B

-6-2 B N N +

6-3 N N B

-7-P1 N N B

-7-P2 N N B

-7-P3 N N B

-7-P4 N N B

-7-P5 N N B

-7-P6 N N B

-7-P7 N N B

-a + or-referstotheabilityorinability, respectively, of

Sc-1cells infected by the particular virus to absorb cytotoxic antibody toGx.Thesedata are taken from Hopkins et al.

(10).

b"Slower"or"faster" refersto therelative electropho-retic mobilities of SP-Nand LP-B virus p15,p30,andgp7O proteins.

e- Electrophoretic mobility of the gp7O of recombinant 5-1has not yetbeen determined.

ating during isolation of the XLP-N viruses

wereforN-tropism and largeXC plaque

mor-phology, then the data presented above have

several implications of biological interest. (i)

That anN-tropic virus may possesap15orgp70

proteinlike that ofaB-tropic virusimpliesthat

tropism does not reside ineither of these

pro-teins (10, 13, 17).

(ii) That some XLP-N viruses, all of which

make large XC plaques, appear to possess a

gp7O derived from SP-N, which makes small

XC plaques, suggests that large XC plaque

morphology is not determined solely (ifatall)

by gp7O (10). However, thatsomany

recombi-nants inheritedgp70fromLP-Bmightsuggest

that thedeterminants(s)ofplaque morphology

lies nearthe genecoding for gp7O. (Note that

these results donotexcludethepossibility that

gp70 is involved in the formation of XC cell

syncytia.)

(iii) One interpretation of the observation

that all of the recombinants studied sofar

in-heritedap30thatcomigrateswithp30ofSP-N

is that N-tropism might be determined by a

gene that is closely linked to p30. We have

obtained other evidence consistent with the

possibility that p30 itself, or a gene closely

linkedtop30,might beadeterminant of N- and

B-tropism: murine leukemia virus variants

thatgrowequallywellonN-and B-typemouse

cells can be obtainedby forced passage ofa

B-tropic virusthrough N-type cells in vitro. The

resultingvirus iscalled NB-tropic(1, 11).Eight

NB-tropic viruses independently derived from

the B-tropic virusof BALB/c by serial passage

onNIH Swiss mouse cells have been found to

possess ap30 with altered electrophoretic

mo-bility on SDS gels (11). One of the eight

pos-sessedanaltered p15inaddition (unpublished

data). Both the apparent linkage of p30 and

N-tropism inthe present studyandthe

observa-tionof an altered- p30inNB-tropic viruses could

be explained in a number of ways that are

unrelated or only indirectly relatedto the

tro-pism of the viruses (see 21). However, it is

interesting to note that the possibility that a

protein present in virions may be a

determi-nantof N-orB-tropismis implied by the

stud-ies of Rein etal. (24) and Bassin et al. (4).

Since RNA tumorviruses arepolyploidand

canform heterozygotes (30), an alternative

ex-planation to recombination for the results we

have presented might be that XLP-N viruses

are stable heterozygotes of SP-N and LP-B

ge-nomes and selectively express, or package,

someproteins coded by one genome and some

codedby the other parentalgenome. Evidence

that XLP-N viruses are recombinants that

in-herited only some oftheir genes fromtheir N

virus parent andothers from their B virus

par-entcomes fromanalysisof theRNase

Ti-resist-antoligonucleotides derivedfrom theRNA

ge-nomes of parental and recombinant viruses

(Faller and Hopkins, unpublished data). This

analysis reveals great similarity between the

genomesof the N-andB-tropicvirusesderived

from BALB/c;ofapproximately35unique

oligo-nucleotides generated by RNase T1 cleavage

andtwo-dimensionalgel electrophoresis, about 30appear to besharedbetween the two viruses.

However, eachparental virus possesses sixor

seven distinctive oligonucleotide "spots," and

the XLP-Nviruses that havebeenanalyzedso

farhavebeenshowntopossessdifferent

combi-nations of N and B specific spots.Thesimplest

interpretationofthis result is thatXLP-N

vi-ruses aregeneticrecombinants assuggestedby

the biologicalevidence (12), antigenic analysis

(10), andthestudy described above.

ACKNOWLEDGMENTS

These studies are basedonobservations made byNancy Famulari and ErwinFleissner, Sloan Kettering Institute.

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VIRION PROTEINS OF N- AND B-TROPIC VIRUSES 707

Wethank Dr. Famulari for many helpful discussions and forcommunicatingunpublished data.

This work was supported by Public Health Service grants from the National Cancer Institute (CA 19308 to N.H., CA 17007 to R.H., and CA 14051 to theCenter for Cancer Research, MIT) and a PublicHealth Service grant from the National Institutes of Health,Biomedical Sciences Supportto MIT(RR 07047 toN.H.).

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2. Baltimore, D. 1974. Tumor viruses: 1974. Cold Spring HarborSymp. Quant. Biol. 34:1187-1200.

3. Barbacid, M., J. R. Stephenson, and S. A. Aaronson. 1976. Gag gene ofmammalian type-C RNA tumor viruses.Nature (London) 262:554-559.

4. Bassin, R. H., B. I. Gerwin, G. Duron-Troise, S. Gis-selbrecht, andA.Rein. 1975. Murine sarcoma virus pseudotypes acquire a determinant specifying N or B tropism fromleukemia virusduringrescue.Nature (London) 256:223-225.

5. Blattler, D. P., F.Garner, K. van Slyke, and A. Brad-ley. 1972. Quantitativeelectrophoresis in polyacryl-amidegelsof 2-40%. J.Chromatogr.64:147-155. 6. Fleissner. E. 1971. Chromatographic separation and

antigenicanalysis of proteins of the oncornaviruses. I. Avianleukemia-sarcoma viruses. J. Virol. 8:778-785.

7. Hartley, J. W.,and W. P. Rowe.1975.Clonal cell lines from aferal mouse embryo which lack host-range restrictions for murine leukemia viruses. Virology 65:128-134.

8. Hartley,J.W.,W. P.Rowe,and R.J. Huebner. 1970. Host-range restriction of murineleukemia virusesin

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large polypeptide precursor ofavian oncornavirus proteins. Proc.Natl. Acad. Sci. U.S.A. 70:1734-1738. 30. Weiss, R. A., W. S. Mason, and P. K. Vogt. 1973. Genetic recombinants and heterozygotes derived from endogenousand exogenous avian RNA tumor viruses.Virology52:535-552.

VOL. 23, 1977

on November 10, 2019 by guest

http://jvi.asm.org/

Figure

FIG.1.phorylase2teinstons;andrase,blue. and Comparison of p30 and p15 virion pro- ofparental viruses SP-N and LP-B
FIG. 2.proteins;LP-Band Comparison of gp7O protein of SP-N and viruses. Autoradiogram of '4C-labeled virion 8 to 20% slab gel
FIG. 4.4-1;Coomassie Comparison ofp30 protein of SP-N, LP-B, and recombinants. An 8 to 24% slab gel stained with brilliant blue
FIG.5.5,contaminating6-3;Coomassie 5-3; Comparison ofp15 protein of SP-N, LP-B, and recombinants
+2

References

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