452 H, FRAENKEL-CONRAT 



qualitative and quantitative aspects of its infectivity and for its resistance to 

 degradation. Tlie most important question is, however, the nature of tlie 

 protein coat of virus originatmg from an infective nucleic acid applied in a 

 "foreign" protein coat. Does the nucleic acid carry the complete genetic 

 information, even includmg every structural detail of its less important 

 partner, and is the plant cell not confused by the presence of the other 

 protein? Serological and preliminary amino acid analyses attest to the 

 complete and infallible domination by the nucleic acid. But detailed and 

 exact amino acid analyses are required (and are as yet in progress) to estab- 

 lish more firmly the identity of the original with the mixed-virus progeny 

 protein. 



B. Mixed Nucleic Acid Viruses 



In the light of present knowledge, no genetic effects were to be expected 

 from the above mixtures of protein and nucleic acid from two strains. How- 

 ever, it seemed that this could possibly be achieved if nucleic acid from two 

 strains could be incorporated artificially into one virus particle through the 

 reconstitution reaction. This was conceivable only if the nucleic acid occurred 

 in the form of active subunits in solution, several of which entered into each 

 particle. Such was the author's concept, but it w^as in conflict with that of 

 Gierer and Schramm (1956; Gierer, 1957), who postulated that only intact 

 complete virus-nucleic acid complements or cores, of about 2 X 10^ mole- 

 cular weight were infectious. Of such units, naturally, no more than one 

 could ever occur in one 300-m/x particle, containing 5-6 % nucleic acid. While 

 the question of the actual minimal molecular weight of the active unit caimot 

 be regarded as settled, it seemed advisable to attack the above problem 

 experimentally. The resulting data should in any case contribute information 

 concerning the nature of the active unit. 



Thus, a considerable number of experiments were performed in which 

 TMV-KNA vras mixed with various other nucleic acids, and subsequently 

 reconstituted with TMV-protein at a constant excess (a 20-fold amoimt of the 

 total nucleic acid) (Fraenkel-Conrat and Singer, 1958b). The various nucleic 

 acids used for mixing (HR-ENA, inactivated TMV-RNA, yeast RNA) had 

 very little, if any, affinity for this protein, and alone gave very few or no 

 lesions upon reconstitution. The results of all these experiments can be briefly 

 summarized as follows: When the two nucleic acids were in contact at low ionic 

 strength, prior to addition to protein and buffer, and when the ballast nucleic 

 acid comprised 70 to 90 % of the mixture, then the reconstituted activity of 

 the TMV-RNA was greatly depressed (usually to about 40 % of the activity 

 given by it upon undiluted reconstitution). Control tests showed that there 

 was no inactivating action of any of these RNA preparations on the direct 



