RNA-synthesizing activities (RNA-SAs) by its nature identical with primase activities (Pr-As) were found to be constantly present in avain myeloblastosis virus (AMV) core isolates. Their endogenous templates are molecules of the virus core-bound host cell DNA (AMV DNA) (Ríman and Beaudreau, 1970) that have been recently recognized as a collection of still active early replicative structures (Ríman et al., 1993b). Like the Pr-As, the RNA-SAs are not inhibited by alpha-amanitin nor by aphidicolin and they show a mutually competitive affinity for ATP and GTP. Their reaction products treated with DNase I are short RNAs similar in length to initiator RNAs (iRNAs), their precursors and degradation products. In AMV core proteins separated in isopycnic CsCl gradients, they are chiefly located in the density region of reverse transcriptase activities (RT-As) but with a distinct peak fraction. Like Pr-As, they are able to use poly(dT) as template and to form, in the presence of [alpha-32P]ATP, products that after DNase I treatment consist of poly(rA) molecules similar in length to iRNA monomers and multimers. Like the Pr-As, they are able to complement E. coli DNA polymerase (pol) I reactions. They occur in the analyzed AMV core proteins as six distinct sedimentation species (PrA-SS). This, together with other relevant properties, indicates the presence of Pr-As associated with molecules of a primase-alpha DNA polymerase enzyme complex, its degradation products and 'free' primase monomers.

Institute of Molecular Genetics Academy of Sciences of the Czech Republic Prague Czech Republic