BENZER 



treatment, followed bv electron micro- 

 scopical analysis.'' He found the recon- 

 stituted rods appreciably more labile to 

 SDS than was standard TMV, but 

 after SDS treatment for 10 seconds 

 many rods were partialH' degraded 

 and showed a central strand of ma- 

 terial protruding from the ends, as 

 does standard TMV after 60 seconds 

 of reaction (Fig. 4). These strands 

 disappeared when ribonuclease was 

 added. 



Sinmi7ary.— The preparation from 

 TA4V of protein and RNA fractions 

 which tend to recombine at about pH 

 6 to form a nucleoprotein carrying 

 virus activity (0.1-1 per cent of that of 

 TMV) is described. 



An electron microscopic search re- 

 vealed no TM\^ rods in either of the 

 two component solutions at a concen- 

 tration level thirty fold to three hun- 

 dred fold greater than those at which 

 the reconstituted virus was assayed. In 

 the latter, on the other hand, up to 

 about one-third of the material con- 



271 



sisted of rods of the typical diameter 

 and length of TMV, many, if not all, 

 containing a nucleic acid core. 



The concentration, time, and pH 

 dependence of virus regeneration is 

 that of a typical chemical reaction. 

 Freshly prepared RNA is required for 

 appreciable reaction; degraded RNA, 

 or nucleic acids from other sources, 

 are inactive. 



No inhibition was observed if known 

 small amounts of TMV were added to 

 concentrated solutions of each of the 

 components and subsequently diluted 

 and assayed. 



The evidence thus seems reasonably 

 complete that, under the conditions 

 described, TMV nucleic acid enters 

 into combination with TMV protein 

 subunits and favors aggregation to 

 rods, some of which are of sufficient 

 length and structural integration to 

 carry infectivity. 



The capable assistance of Mrs. B. 

 Singer and A4r. J. Toby is gratefully 

 acknowledged. 



Fine Structure of a Genetic Region in 

 Bacteriophage* 



SEYMOUR BENZER 



Reprinted by authors and publisher's permis- 

 sion from Proceedings of the National Academy 

 of Sciences, vol. 41, 1955, pp. 344-354. 



The technique introduced in this paper, which provides a method 

 of jneasiiring the actual size of a genetic unit by the way the or- 

 ganism reacts iti specified experimejital situations, appears to be quite 



* Supported by a grant-in-aid from the tion of the Committee on Growth of the 

 American Cancer Society upon recommenda- National Research Council. 



