Primer requirement and template specificity of a DNA polymerase of chick embryo.

A DNA polymerase purified from extracts of chick embryo catalyzes the synthesis of poly(dT) in the presence of poly(rA) or poly(dA) as template and poly(dT) or oligo(dT) as primer. Oligo- or polyribonucleotides are relatively ineffective initiators of polydeoxynucleotide polymerization. Using activated DNA as template, the enzyme catalyzes a repair-like reaction that resembles that catalyzed by RNA-directed DNA polymerase of RNA tumor viruses and Escherichia coli DNA polymerase II. With natural templates containing poly(rA) sequences, such as avian myeloblastosis virus RNA or rabbit globin mRNA, and oligo(dT) as initiator, principally poly(dT) is synthesized. Consequently, the enzyme differs from the RNA-directed DNA polymerase associated with RNA tumor viruses by its incapacity to transcribe heteropolymeric regions of RNA templates. The possible role of the enzyme in repair of DNA during transcription is discussed.