186 S. Spiegelman 



were in the neighbourhood of 30 per cent of those obtainable 

 with intact cells. Single burst experiments demonstrated that 

 virus synthesis was occurring in a major proportion of the 

 infected protoplasts. 



That protoplasts do indeed retain a major proportion of the 

 synthetic potentiality of the cells from which they are derived 

 is dramatically exhibited by Salton's (1955) experiments on 

 spores. A modification of Hardwick and Foster's (1952) pro- 

 cedure for "committing" cells to sporogenesis was employed. 

 The cells were then converted to protoplasts with lysozyme 

 and incubated further. Approximately 1 per cent of the 

 protoplasts were thereby converted to viable spores detectable 

 by suitable plating procedures. Thus far no one has achieved 

 direct conversion of protoplasts to viable cells by resynthesis 

 of the cell wall. McQuillen (1955c) has, however, provided 

 evidence indicating that protoplasts are capable of limited 

 division. When properly supplemented, and incubated with 

 aeration for periods extending between four and six hours, 

 protoplasts take on dumb-bell shapes which are highly sugges- 

 tive of the occurrence of incipient division. 



Incorporation Studies 



Attempts to study protein synthesis by tracer methods were 

 actually made prior to the appearance of WeibuU's publication 

 and when it was not realized that under certain conditions 

 treatment of sensitive cells with lysozyme results in the 

 appearance of microscopically visible structural elements. 

 Lester (1953) exposed Micrococcus lysodeikticus to lysozyme 

 in the presence of sucrose and found that such "lysates" 

 could still incorporate ^*C-labelled leucine into the protein 

 fraction. The addition of deoxyribonuclease enhanced the 

 incorporation, whereas ribonuclease abolished it. Similar 

 findings were reported by Beljanski (1954), who used labelled 

 glycine. Here again stimulation with DNAse and inhibition 

 with RNAse were observed. It seems probable that both 

 of these investigators were dealing wholly or in part with 



