SECTION 3 



MOLECULAR AND MICROBIAL GENETICS 



3.1. Further Studies on Incorporation of Homologous 

 DNA into the Mouse Germ Cells in vivo. 

 Chai Hyun Yoon (Chestnut Hill U.S.A.). 



DNA in the thymus glands was tagged with 

 thymidine-H 3 , and the extracted thymus- 

 DNA-H 3 was injected into the gonads of mature 

 male mice. The germ cells of recipient mice 

 were studied with both squash and section met 

 thods for the evidence of thymus-DNA-H 3 

 incorporation in vivo. Quantitative data will be 

 presented. 



3.2. Evidence for the Source of Messenger RNA and 

 the Control of Its Production in the Regulation 

 of Gene Activity. Alfred Marshak (Phila- 

 delphia, U.S.A.). 



Ribonucleic acid from cytoplasm (c-RNA) is 

 so constituted that on treatment with weak 

 alkali all of its constituents are released as 

 nucleotides. In contrast, ribonucleic acid 

 from nuclei of the same or similar cells (n-RNA) 

 when similarly treated yields adenine, guanine, 

 and cytosine and adenosine in amounts equal to 

 the nucleotide released. The release of these 

 bases is correlated with the presence of material 

 extractable in lipid solvents which renders the 

 ribosidic bonds susceptible to alkali hydrolysis. 

 When both components of n-RNA are accounted 

 for, it is found to have base ratios resembling 

 those of DNA. The component of n-RNA not 

 associated with lipid has ratios similar to those of 

 c-RNA. Previously it was shown that n-RNA is 

 the precursor of ribosomal RNA. The present 

 experiments indicate that it contributes to the 

 ribosomes that portion of its nucleotides which 

 are not associated with lipids. The n-RNA thus 

 has the properties required of a source of mes- 

 senger RNA. It is proposed that the association 

 of lipid or lipoprotein with the n-RNA provides 

 a mechanism for the control of gene activity 

 through regulation of the release of messenger 

 RNA from n-RNA or by other means. 



3.3. The Structure of Adapter RNA. Geoffrey 

 Zubay (Upton, U.S.A.). 



Adapter RNA is the carrier of amino acids to 



the template for protein synthesis. Part of its 

 function is to arrange the amino acids in a 

 specific order prior to peptide synthesis. It does 

 this by the following means: each adaptor 

 combines with one — and only one — amino 

 acid; and each adaptor is presumed to have a 

 trinucleotide sequence which hydrogen-bonds 

 to a complementary site on the messenger 

 RNA template. Physico-chemical measure- 

 ments indicate that adapter RNA is a single 

 polynucleotide chain about 67 nucleotides long. 

 It has been proposed that the polynucleotide 

 chain has a bend near the middle, with the two 

 halves of the chain interacting in double helical 

 fashion. to In a more recent and detailed model, 

 it has been suggested that the only nucleotides 

 not in the double helix configuration are the 

 three in the bend, and the two on the nucleoside 

 end which combines with the amino acid.(' 2 ) 

 This structure will be discussed with regard to 

 (1) stereochemical problems of protein syn- 

 thesis^ 23 ) and (2) chemical methods for demon- 

 strating the location and composition of the 

 coding nucleotides. ( 4 ) 



Research carried out at Brookhaven National 

 Laboratory under the auspices of the U.S. 

 Atomic Energy Commission. 



1. G. Brown and G. Zubay, /. Mol. Biol. 2, 

 287, 1960. 



2. G. Zubay and J. Bergeron, Symp. A-II-I, 

 8th Intern. Microbiology Congr., Montreal, 

 1962, in press. 



3. G. Zubay, Science, in press. 



4. G. Zubay, Biophys. Biochem. Res. Commtin., 

 in press. 



3.4. The Genetic Implication of the Methylated Bases 

 in Transfer RNA. Erwin Fleissner, P. R. 

 Srjnivasan and Ernest Borek (New York, 

 U.S.A.). 



Transfer RNA is characterized by the unique 

 presence of a small number of methylated 

 purines and pyrimidines. The origin of these 

 methyl derivatives has been obscure until re- 

 cently. We have shown that the methylated bases 



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