THE SURFACE OF VIRFSES 



131 



of infoctivity of TMV as sliowu in Fig. 5.."». 'I'lic iiiliihition of 

 infectivity is reversible, as sliown by diluting a 4 : 1 combination 

 of virns and polypeptide. When dilnted, the virus-poly pei:)tide 

 combination evidently loosens, as the infectivity returns to 

 normal at low concentrations. 



In the second paper, the process is studied in more detail 

 with the electron microscope and with a quantitative method of 



100 



100 200 



Polypeptide Concentration 



300 



Fig. 5.3. Reduction of infectivity of TMV by lysine polypeptides in various 

 concentrations according to tlie data of Stahmann, Graf, Patterson, Walker, 

 and Watson (1951). 



determining the amount of precipitate formed when virus and 

 polypeptide are mixed. In addition, they carried out studies 

 of the amount of virus-polypeptide precipitate formed when 

 the pH is varied. Their results show that: 



(a). The virus infectivity is reduced before a precipitate 

 between virus and polypeptide is formed. 



(6). No precipitation occurs at 2>H2 or pHlO. This is the 

 region in which both the virus and the protein carry a net 

 charge of the same sign. 



