Complexity of nuclear and polysomal RNAs in growing Dictyostelium discoideum cells

Abstract

As a first step in quantitating gene expression during differentiation of Dictyostelium discoideum, we have measured the complexity of polysomal, cytoplasmic, and total cellular polyadenylated RNA in growing cells. We have employed two different types of RNA excess hybridization reactions: kinetic cDNA-RNA and saturation single-copy genomic DNA-RNA hybridization. Both types of measurements indicate that about 4000 to 5000 different mRNA-sized, polyadenylated sequences are found in the cytoplasm in greater than one copy per cell. All of these are present on polysomes. These sequences correspond to the expression of 19% of the single-copy portion of the genome. Polyadenylated transcripts of an additional 9000 averaged-sized genes are found in the nucleus, but are transferred very poorly, if at all, to the cytoplasm. These nuclear polyadenylated RNA species corresponded to the expression of an additional 34% of the single-copy portion of the genome.