286 ELLIOT VOLKIN 



19G1), the protein iJiodiiccd hy some of tlic ildiihic iiiiit;iiit> lias l)C'cn 

 altered in amino acids tlirouii;li the Icii^tli of the polypcplidc chain 

 corresponding; to the region between the two alterations in the DNA 

 chain. 



VIII. Summary 



An RNA of composition siniihir to DNA has been detected in a 

 number of different l)iologic systems. Its presence in pluige-infected 

 bacteria is particularly ajjparent, since ribosomal RNA synthesis is 

 preventeci in that systeuL This RNA jirobably has a sedimentation 

 constant of 12-14S but aj^pears to be largely reversibly associated with 

 ribosomal pai'ticles. The RNA undergoes rapid turnover, which can be 

 measured by its molecular degradation in the ])hage-infected cell, and 

 by its translocation to other subcellular components in actively growing 

 bacteria. The turnover phenomenon seems to be part and parcel of its 

 function as deduced fi"om kinetic studies. Moreover, by cori'elating the 

 amount of such RNA synthesis witli (/) phage ])i-oduction, (2) enzyme 

 synthesis, and (5) i?} intro amino acid incorporation, a definite stoichi- 

 ometry has been found to exist between the amount synthesized and the 

 protein product. Specific RNA-DNA hybrids (where the RNA has a 

 composition similar to the DNA) can be isolated from extracts, as well 

 as produced by "annealing" of RNA with only the homologous DNA. 

 RNA of DNA-like composition likewise can be synthesized iti vitro 

 with the enzyme, RNA polymerase. RNA synthesized in this manner 

 markedly activates the incorporation of amino acids into protein in 

 cell-free systems. In all probability such in m'^ro-synthesized, complete, 

 RNA molecules will be shown eventually to be capable of directing the 

 synthesis of complete, biologically active proteins. Presently, however, it 

 is possible to use synthetic polynucleotides to demonstrate the existence 

 of a definite specificity between the nucleotide composition and the 

 particular amino acid incorporated into protein. In this way, a partial 

 nucleotide triple code for most of the naturally occurring amino acids 

 has been resolved. 



References 



A.straclian, L. (1960). Fcdcmiion Proc. 19, 198. 



A.strachan, L., and Fisher, T. N. (1961). Federation Proc. 20, 359. 



A.strachan, L., and Volkin, E. (1958). Biochim. el Biophys. Ada 29, 536. 



A.strachan, L., and Volkin, E. (1959). Biochim. et Biophy.f. Ada 32, 449. 



Bautz, E. K. F., and Hall, R. D. (1962). illh Annual Mcding Bi,>phi/.'<. Sor.. Wash- 



inglon, D.C. Abstr. TA8. 

 Bessnian, M. J. (1959). ./. Biol. Clwm. 234, 2735. 



