The broad objectives of this proposal are to study the biogenesis of messenger RNA and its post-transcriptional modification by poly A polymerases. The experimental approach will examine heterogeneous nuclear RNA (HnRNA), its synthesis and processing into messenger RNA in a cultured myeloma cell line which produces a specific messenger RNA for the light chain polypeptide of immunoglobins. Preparations of nuclei from myeloma cells which synthesize RNA in vitro will be used to study the polyadenylation of HnRNA and its processing into mRNA and the release of mRNA from the nucleus. A second phase of the proposal will be devoted to polyadenylation reactions with purified poly A polymerases. Purification of this polymerase from calf thymus by affinity chromatography is planned. A study of structural features associated with the ability of RNA molecules to function as primers for poly A polymerase is also planned. Localization of the polymerase in the cytoplasm or nucleus of cultured HeLa and myeloma cells is being investigated.