Cotton messenger RNA sequences exist in both polyadenylated and nonpolyadenylated forms

The physical characteristics and sequence content of polyadenylated and nonpolyadenylated messenger RNAs were determined in total and polysomal RNAs isolated from cotton cotyledons after 24 h of germination. RNAs were fractionated on the basis of their poly(A) content by passage through poly(U)-agarose. The mass average size of poly(A) is 112 +/- 4 nucleotides in total RNA and 81 +/- 3 nucleotides in polysomal RNA. Less than 2% of the poly(A) tracts are between 5-15 nucleotides in length. The mass average length of recovered polyadenylated mRNAs from either RNA is 1600 nucleotides. In vitro translation of the RNAs in the wheat germ system and hybridization of the RNAs with complementary DNAs confirmed the physical estimates of their absolute amounts. About 3.3% of the high molecular weight RNA in the tissue is mRNA, of which 40% is on polysomes. Abut 45% of the polysomal mRNA and 75% of the nonpolysomal mRNA is polyadenylated. These mRNAs are transcribed from nonrepetitive DNA. Both techniques unambiguously demonstrate that all mRNA populations contain the same sequences in about the same relative concentration. At this point of development in this tissue, differential polyadenylation or entry into polysomes cannot be specific for particular mRNA sequences.