Polyadenylate metabolism in the nuclei and cytoplasm of Saccharomyces cerevisiae

Abstract

A procedure has been designed for the simultaneous isolation, in a single step, of the nuclei and cytoplasm of Saccharomyces cerevisiae alphas288c spheroplasts. We have examined the polyadenylate poly(A)-containing RNA in these fractions and their kinetics of synthesis. Nuclear RNA saturates with [3H] adenine within 10 min. Labeled RNA appears very quickly in the cytoplasm, exceeding the amount of labeled nuclear RNA within 2 min after the addition of [3H] adenine. Nuclear poly(A)-containing RNA is approximately 10% of the total cellular poly(A)-containing RNA obtained from spheroplasts labeled for 15 min. Nuclear poly(A)-containing RNA is not as large as the giant heterogeneous nuclear RNA of animal cells. The distribution of molecular size in nuclear and cytoplasmic populations of poly(A)-containing RNA is very broad with the average size of the nuclear species being moderately larger than the cytoplasmic species. Three distinct size classes of poly(A), with different apparent kinetic properties, are obtained from yeast poly(A)-containing RNA. Their electrophoretic mobility suggests molecular lengths of approximately 20, 40, and 60 nucleotides (Groner, G., Hynes, N., and Phillips, S. (1975) Biochemistry, 13, 5378-5383). Each of these poly(A) classes are present in the mRNA from large and small polyribosomes.