The synthesis and characterization of homopolynucleotide sequences both poly A and oligo A as well as oligo U sequences are being investigated in cultured HeLa cells to characterize the basic properties of these sequences and to use them to study the metabolism of the heterogeneous RNA of the nucleus and the messenger RNA of the cytoplasm. The ultimate goal of the project is to discover the function of these sequences, as well as the mechanism of their biosynthesis. A detailed study of a highly purified poly A polymerase from calf thymus nuclei is in progress to establish the mechanism of this reaction and the sites of specificity for the polynucleotide primer required for poly A synthesis. A poly A polymerase is being investigated in cultured Hela cells.