Direction of Polymerization by the Avian Myeloblastosis Virus Deoxyribonucleic Acid Polymerase

Abstract

An oligonucleotide primer is necessary to initiate polymerization of nucleotides by the DNA polymerase of avian myeloblastosis virus. The role of the primer was investigated by synthesizing the acid-soluble oligonucleotide [5'-^(32)P](dT)_(10). Conversion of this primer to an acid-insoluble form by the DNA polymerase in the presence of poly(A) indicated that the primer was physically incorporated into the product. The phosphate residue at the 5'-terminus of the primer remained sensitive to alkaline phosphatase, and synthesis therefore appeared to proceed by addition of mononucleotides at the 3'-OH of the primer. Inhibition of DNA polymerase activity by dideoxythymidine triphosphate was observed using templates containing AMP or when the enzyme was copying the viral RNA found in the virion. Copying of poly(C) by the DNA polymerase was not sensitive to the analogue. These results corroborate the conclusion that the polymerase adds nucleotides to the 3'-OH of a primer and further indicate that copying of the endogenous viral RNA involves only polymerization on 3'-OH groups.

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