BIOLOGICAL ASPECTS OF INTRACELLULAR STAGES OF VIRUS GROWTH 145 



that both viruses showed similar behavior on adsorption to, and subsequent 

 elution from, chick red cells. In addition, Svedmyr (1949) found similar 

 enzymatic activity of both forms in their ability to destroy the inhibitor 

 present in normal allantoic fluid. From present information, therefore, 

 incomplete and standard virus have a similar surface structure and the 

 difference between them is a more fundamental one. 



One difference which was noted early in a careful comparison of standard 

 and incomplete virus was in their sedimentation behavior in the high-speed 

 centrifuge (Gard et al., 1952). Standard virus consisted for the most part of 

 rather homogeneous particles with a sedimentation constant of 747 A. In 

 highly incomplete virus preparations the 747 S component was replaced by a 

 very inhomogeneous slower sedimenting component of sedimentation 

 constant varying from 430 to 675 S. As mentioned earlier, there was not 

 sufficient morphological difference between particles of standard and incom- 

 plete virus seen in electron micrographs to account for the different sedimenta- 

 tion behavior, and a difference in particle density appeared to be the most 

 likely explanation. Support for this came from a study by Uhler and Gard 

 (1954), who found that incomplete virus had a higher lipid content than 

 standard virus. From a preliminary analysis of the lipid content of prepara- 

 tions showing varying degrees of incompleteness, it was concluded that the 

 findings could not be explained by postulating virus of low and high lipid 

 content, i.e., there was some variability in the lipid content among different 

 virus particles. These findings might, therefore, account for the unusual sedi- 

 mentation behavior of incomplete virus, but, at the moment, there is no 

 explanation for the difference in lipid content in terms of mechanisms of viral 

 synthesis, nor is it clear what is the influence, if any, of the lipid content of the 

 virus particle on its infectivity. 



More pertinent to the problem of the infectivity of incomplete virus is the 

 work of Ada and Perry (1956) on the nucleic acid content of preparations of 

 influenza virus showing varying degrees of incompleteness. In a most 

 important study, these workers showed that when the infectivity of different 

 preparations (expressed as log infectivity titer/agglutination titer) was 

 plotted against its nucleic acid content a linear relation was found. There was 

 no simple proportionality between infectivity and nucleic acid content and a 

 hundred-fold decrease in infectivity was accompanied by a drop in RNA 

 content from about 1 % to 0.5 %. It is interesting to note that Lief and 

 Henle (1956b) found a very similar ratio between the amount of "soluble 

 antigen" (see Section III, A) which could be extracted from incomplete 

 virus by ether treatment and the 1/HA ratio of the virus used, i.e., there 

 appears to be a close relationship between the soluble antigen content and the 

 nucleic acid content of the virus. The proportions of the nucleotide bases in 

 the study by Ada and Perry were not significantly different in incomplete and 



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