Multiple oligo(A) tracts associated with inactive sea urchin maternal mRNA sequences

Abstract

Maternal RNA of sea urchin eggs and embryos was analyzed for short poly(A) sequences by digesting hybrids formed between [ 3H]poly(U) and poly(A) with RNase at 4°C. When the undigested [ 3H]poly(U) is precipitated with CTAB, all (A) n tracts longer than 6 nucleotides are detected. This assay revealed a poly(A) content severalfold higher than is obtained with a similar assay using RNase at higher temperatures. On polyacrylamide gel electrophoresis, most of the previously undetected (A) n tracts ran as a peak of oligo(A) of less than 20 nucleotides which accumulated at the dye front. The oligo(A) sequences were resolved into a single peak of (A) 10 when sized on Sephadex G100. These (A) 10 sequences were associated with large mRNA-sized molecules of about 3000 nucloetides average length which comprised 0.5 to 2% of the total maternal RNA. However, the (A) 10 sequences were not in mRNA molecules containing 3′-terminal poly(A) of 50–120 nucleotides nor did they remain in RNA that entered polysomes upon fertilization. However, hybridization studies showed that all sequences represented in the maternal poly(A)-containing RNA appeared to be present in the RNA molecules containing only (A) 10 sequences. The results suggest that the (A) 10-containing RNA might be incompletely processed mRNA precursor-like molecules.