Sequence divergence of nucleus-confined polyadenylated ribonucleic acids in Friend erythroleukemic cells

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Abstract
For determination of whether any potential protein-coding RNA sequences are confined to the nucleus in [murine] Friend cells, a comparison was made of the sequence divergence of polyadenylated RNA molecules which are either nucleus confined or transported to the cytoplasm. Both unique DNA and cDNA probes enriched in such sequences were reacted with a large excess of mouse or rat DNA. The extent of hybridization and the thermal stability of hybrids formed under various stringency conditions were used as a measure of the amount of sequence divergence which had taken place. The results confirmed that messenger sequences are relatively conserved during evolution. Experiments involving both unique DNA probes representative of the full length of nucleus-confined RNA molecules and cDNA probes complementary to their poly(A)-adjacent fragments indicated that the polyadenylated nucleus-confined sequences have on average diverged during evolution much more than mRNA sequences. The vast majority of these sequences probably do not represent potential mRNA which are confined to the nucleus and subject to posttranscriptional control in a manner similar to those which have been demonstrated in sea urchins.