504 



A. TSUGITA AND H. FRAENKEL-CONRAT 



TABLK IT {Conliniied) 



° Besides these 27 strains showing differences from common TMV, which in most 

 instances were confirmed also bj' the analyses of progeny isolates, 29 other strains 

 showed no detectable differences in composition from the parental strain. 



* Not known whether aspartic acid or asparagine residue. 



" Secondary change from strain 237. 



'' Secondar}' change. 



' Propylene oxide. 



volved not the same near C-terminal pi'oline previously reported to be 

 replaced in 1 nitrous acid mutant (Tsugita and Fraenkcl-Conrat, 1960) ; 

 and 1 particular serine (#138) was found replaced by phenylalanine in 

 1 methylation and 2 deamination mutants. These data are summarized 

 on Table II. 



A survey of the location of changes on the peptide map indicates that 

 these occur at sites scattered over the entire sequence. Where multiple 

 changes were observed, these were not in vicinal j'jositions. While the 

 total number of located changes is too small to justify any far-reaching 

 conclusions, it would appear from the data illustrated in Fig. 7 that the 

 distal parts of the peptide sequence are more prone to change than the 

 central ones. It must be stressed, however, that this may have no genetic 

 cause but be due to selection, in that mutation resulting in the exchange 

 of specific amino acids might not give a functional or stable protein, and 



