thiouracil (Amos and Vollmayer, 1958)» Haemagglutinin production is still affected as late as 16 hours after infection.

In document The use of inhibitors in the analysis of the growth cycle of vaccinia virus (Page 163-167)

Sunakawa, 1956; Hershey and Melechen, 1957) In the presence of chloramphenicol, the destruction of the b acterial nucleus

by 2- thiouracil (Amos and Vollmayer, 1958)» Haemagglutinin production is still affected as late as 16 hours after infection.

The effect is reversed by uracil completely up to 8 hours after

addition of the virus but not at all after 10 hours. These

workers have shown that there is an increase in the incorporation of g u a n i n e - C ^ and ^ P - phosphor us into the RNA of cells after infection and that this incorporation is inhibited by the presence

of thiouracil. It was noted that the ratio of infectivity to

haemagglutinin was 50$ lower in the presence of thiouracil so that incorporation of thiouracil may have occurred in to the RNA of the virus with the consequent production of non-infeetious particles.

Complete suppression of the growth of poliovirus in monkey-testicular cultures for up to 12 days is similarly produced by thiouracil and other substituted pyrimidines (Knox et al., 1957)*

Protein,

The presence of an amino acid analogue prevents the incorporation of all amino acids including the homologue into

the proteins of bacteria (Halvorson and Spiegelman, 1952). In

Ehrlich ascites tumour cells, thienylalanine, o-fluorophenyl- alanine and ethionine act as competitive substrates rather than

inhibitors of protein synthesis. These amino acids are incorpo­

rated into the protein and do not inhibit the incorporation of amino acids other than their corresponding metabolites into

proteins (itabinovitz, Olsen and Greenberg, 1954). o-methyl-

threonine, however, inhibits the incorporation of other amino

acids as well as its competitive substrate, isoleucine. Thus two

modes of action of analogue antagonists can be detected, one of

which involves incorporation of the analogue into protein. It

depends on the extent of incorporation and the particular antagonist whether the resulting protein is still biologically active.

a) Methoxinine. This amino acid analogue inhibits the multi­ plication of influenza A virus in surviving chorioallantoic

membranes (Ackermann, 1951). Virus multiplication is completely inhibited when "the compound is added at 1 or 2 hours, while no effect is observed at 6 hours. Partial inhibition is produced by addition at 3 or 4 hours (Ackermann and Maassab, 1954). The

106 compound i s m ost e f f e c t i v e d u r in g th e f i r s t t w o - t h i r d s o f th e l a t e n t p e r io d b u t h a s some i n h i b i t o r y e f f e c t d u r i n g th e l a s t t h i r d . The i n h i b i t o r y e f f e c t i s b lo c k e d by L -m e th io n in e b u t n o t by D -m e th io n in e an d t h i s s u g g e s ts t h a t L -m e th io n in e i s in v o lv e d i n th e b i o s y n t h e s i s o f i n f l u e n z a v i r u s (A ckerm ann, 1951)* b ) p - F lu o r o p h e n y la la n in e (FPA ). FPA i n h i b i t s th e m u l t i p l i c a t i o n o f p o l i o v i r u s a t a n e a r l y s ta g e a n d t h i s i n h i b i t i o n i s c o m p le te ly r e v e r s e d by th e a d d i t i o n o f th e hom ologue, p h e n y la la n in e

(A ckerm ann, R ab son and K u r tz ,

1954

)* S u p p r e s s io n of m u l t i p l i c a t i o n i s c o m p le te o n ly when th e i n h i b i t o r i s ad d ed a t 1 o r 2 h o u rs a f t e r th e v i r u s and FPA h a s no e f f e c t when ad d ed a f t e r 4 o r 5 h o u r s . A lth o u g h th e compound i n h i b i t s th e m u l t i p l i c a t i o n o f p o l i o v i r u s , i t d o es n o t a f f e c t e i t h e r th e tim e o f a p p e a ra n c e o r th e s e v e r i t y o f th e c y t o p a t h i c e f f e c t s p ro d u ced by p o l i o v i r u s i n t i s s u e c u l t u r e . Ackermann e t a l . (

1954

) c o n c lu d e d t h a t th e p r o c e s s e s l e a d i n g t o v i r a l in c r e a s e an d c e l l u l a r i n j u r y p o s s e s s a c e r t a i n d e g re e o f autonom y. The e f f e c t o f FPA on th e m u l t i p l i c a t i o n o f i n f l u e n z a v i r u s was i n v e s t i g a t e d by Ackermann and M aassab (1 9 5 5 ) an d com pared w ith t h a t o f m e th o x in in e . Some d i f f e r e n c e was o b s e rv e d i n t h e b e h a v io u r o f t h e s e tw o a n a lo g u e s a n d i t was s u g g e s te d t h a t two r e a c t i o n s sire o c c u r r i n g i n th e l a t e n t p e r i o d o f in f l u e n z a

multiplication. The first of these begins early in the latent

period and is inhibited by methoxinine and not by FPA; the

second is sensitive to FPA and not to methoxinine. The latter

reaction cannot proceed unless the first reaction is occurring

or has operated for some prior interval. The results showed

that FPA is 93$ effective up to 4 hours while methoxinine is only

partially effective (7y/o) at this time ; both are ineffective

after 7 hours. Similarly whereas removal of FPA results in an

immediate rise in the titre of infectious virus, there is a 2 hour lag after removal of methoxinine before a similar rise is

apparent. They suggested that these inhibitors may differentially

inhibit nucleic acid and protein synthesis. The product of the

FPA sensitive reaction according to Uhlendorf (1957) is a non- haemagglutinating viral antigenic material whose conversion to haemagglutinating material cannot proceed in the presence of the inhibitor.

Fowl plague virus is closely related to influenza virus and the effect of FPA on this virus has been investigated in

detail by Zimmermann and Schäfer (i960). They were able to

demonstrate the existence of several discrete steps in the multiplication of this virus on the basis of susceptibility to

the inhibitor. When FPA is added before or within one hour of

1— — *

108

although the virus is eclipsed in the cell in the normal fashion. The production of S-antigen proceeds normally when FPA is added 2 hours after infection but the production of haemagglutinin and

infectious virus is completely suppressed. Addition of FPA

between 3 and 6 hours after infection results in a diminishing

In document The use of inhibitors in the analysis of the growth cycle of vaccinia virus (Page 163-167)