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

Abstract

The base-sequence complexities and relative abundance of polysomal and nuclear polyadenylated [poly(A+)] RNA sequences were 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 .times. 106 K base pairs). By hybridization with specific c[complementary]DNA, 3 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 .times. 103, 0.9 .times. 103 and 14.5 .times. 103 kilobases. This corresponds to 7000-8000 mRNA species of an average length of 2000 nucleotides, present on an average of 5-600 copies/cell. In nuclear RNA, a major class of abundance was found with a complexity of 100 .times. 103 kilobases, each sequence being present in 1 copy/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 in the nuclear or polysomal compartments of embryonal carcinoma cells, even at levels that would have detected 1 sequence/50 cells.