Studies on polynucleotides

Repair replication of short synthetic DNA's corresponding to parts of the gene for the major yeast alanine transfer RNA has been studied. The enzymes used were the Escherichia coli, Microccua luteus and T4 DNA polymerases, similar results being obtained with all the three enzymes. The DNA's used (Fig. 1) were: four double-stranded DNA's with the termini containing the 5′-hydroxyl group protruding by one, three, four or ten nucleotide units and two single-stranded DNA's 29 units long which are capable of folding back on themselves. The aspects inve tigated were: (1) completion of repair, (2) the minimum size of the polynucleotide chains required as primers and those which can serve as templates and (3) the minimum size of the primers which can abolish hairpin formation so as to give the “normal” repair replication. Repair replication of DNA's (DNA-I to DNA-IV: Fig. 1) was characterized to be essentially complete. The minimum size of the primer for repair replication of an extended single-stranded deoxypolynucleotide was ascertained to be about five to seven units long, while the primers required to overcome the hairpin formation in DNA-V and DNA-VI were found to be about twelve units long. Thus, in the presence of a suitable primer, the nucleotide incorporation which occurs in DNA-V in the absence of added primer was completely replaced by incorporation expected for normal repair replication. The minimum size of a chain which can serve as a template was also found in the present work to be about 12 units long.