STEREOISOMERS OF DEOXYNUCLEOSIDE 5'-TRIPHOSPHATES AS SUBSTRATES FOR TEMPLATE-DEPENDENT AND TEMPLATE-INDEPENDENT DNA-POLYMERASES

All four possible stereoisomers of dNTP with regard to deoxyribofurano se C-1' and C-4' carbon atoms were studied as substrates for several t emplate-dependent DNA polymerases and template-independent terminal de oxynucleotidyl transferase. It was shown that DNA polymerases alpha, b eta, and epsilon from human placenta and reverse transcriptases of hum an immunodeficiency virus and avian myeloblastosis virus incorporate i nto the DNA chain only natural beta-D-dNTPs, whereas calf thymus termi nal deoxynucleotidyl transferase incorporates two nucleotide residues of alpha-D-dNTP and extends the resulting oligonucleotide in the prese nce of beta-D-dNTPs. The latter enzyme also extended alpha-anomeric D- oligodeoxynucleotide primers in the presence of beta-D-dNTPs. None of the studied enzymes utilized L-dNTPs. These data indicate that templat e-dependent DNA polymerases are highly stereospecific with regard to d NTPs, whereas template-independent terminal deoxynucleotidyl transfera se shows less stereodifferentiation. It is likely that the active cent er of the latter enzyme forms no specific contacts with the nucleic ba ses of both nucleotide substrate and oligonucleotide primer.