Complexity of nuclear and polysomal polyadenylated RNA in a pluripotent embryonal carcinoma cell line

The base-sequence complexities and relative abundance of polysomal and nuclear polyadenylated [poly(A+)] RNA sequences have been analyzed in a pluripotent embryonal carcinoma cell line. Polysomal RNA and nuclear poly(A+) RNA have a complexity representing respectively 0.5% and 2.5% of the single copy component of haploid mouse DNA (1.8 X 10(6) K base pairs). By hybridization with specific cDNAs, three abundance classes were found in polysomal poly(A+) RNA, representing respectively 31%, 33%, and 36% of the RNA, with base sequence complexities of 0.1 X 10(3), 0.9 X 10(3), and 14.5 X 10(3) kilobases. This corresponds to 7000-8000 different mRNA species of an average length of 2000 nucleotides, present on an average of 5 to 600 copies per cell. In nuclear RNA, a major class of abundance was found with a complexity of 100 X 10(3) kilobases, each sequence being present in 1 copy per nucleus. The majority of the polysomal poly(A+) RNA sequences are represented in the nuclear poly(A+) RNA but are present in a more restricted range of relative abundance implying posttranscriptional mechanisms of quantitative modulation: polysomal RNA sequences appear to be preferentially transcribed into nuclear cDNA suggesting a preferential location of these sequences close to poly(A) sequences. The presence of a specialized gene product, globin specific RNA, could not be detected either in the nuclear or polysomal compartments of embryonal carcinoma cells, even at levels that would have detected one sequence per 50 cells.