480 A. TSUtllTA AN'l) H. FRAKN KKI.-CONKAT 



a molecular ux-ight of about 100.(X)0 (4Sl, corrcsi)on(ling to an aggre- 

 gation product of six molecules (Sclirannn ct (iL, 19ool. The protein as 

 (lisaugi-ciiated carefully 1)V alkali at low ionic strength, shows a molec- 



Fiti. 1. Model of tobacco mosaic structure (Kiug and Caspar, 1960). The model 

 represents protein .subunits (white bodies) aggregated by helical stacking and held 

 together by RNA (black tube). Some protein units (jjeptide chains) have been 

 removed to show the location of the RXA. The segment shown corresponds to 

 about one-tenth of tlic total length, since one virus particle consists of about 2130 

 protein chains (nioleculur weight about 18,000), arranged in 130 helical turns. 



ular weight of 36,000 (Newmark and Alyers, 1957), and at high pH, 

 or in quite dilute solution, or in 67^ acetic acid, the protein shows the 

 molecular weight of 18.000 characteristic for the monomer (Ansevin and 

 LaulTer, 1959; Wittmann, 1959b). The electrophoretic behavior of the 



