Expression of single copy DNA sequences in nuclear RNA from undifferentiated mouse embryonal carcinoma and differentiated muscle cell line.

Nuclear RNA from an undifferentiated mouse embryonal carcionma (EC) cell line and a differentiated muscle (Mt) cell line from similar origin has been analysed with respect to base sequence complexity and frequency distribution with different probes. With the single copy component of mouse genomic DNA it is shown that total EC nuclear RNA and Mt nuclear RNA have respectively base sequence complexities of 100 Kb and 140 Kb corresponding to 6% and 8% of one strand of DNA. It is shown by hybridization with a purified DNA component complementary to total nuclear RNA that nuclear poly A+RNA in both cell types has only one fifth of total nuclear RNA complexity (as has polysomal RNA), but still contains all poly A+RNA present in polysomal poly A+RNA. Polysomal poly A+ sequences in total and poly A+ nuclear RNA are present in a restricted range of frequency distribution in contrast to the situation observed at the polysomal level. The implication of these results in terms of transcriptional and post-transcriptional control is discussed.