title: Structure and function of rat liver polysome populations. I. Complexity, frequency distribution, and degree of uniqueness of free and membrane-bound polysomal polyadenylate-containing RNA populations.
abstract: Free and membrane-bound polysomes were isolated from rat liver in high yields with minimal degradation, cross-contamination, or contamination by nuclear or nonpolysomal cytoplasmic ribonucleoprotein. Poly(A)+ RNA fractions isolated from free and bound polysomal RNA (poly(A)+ RNAfree and poly(A)+ RNAbound) by oligo(dT) cellulose chromatography exhibited number-average lengths of 1,600 and 1,200 nucleotides, respectively, on formamide sucrose gradients. Poly(A)+ RNAfree and poly(A)+ RNAbound contain 9.1 +/- 0.55 and 10.7 +/- 0.50% poly(A) as measured by hybridization to [3H]poly(U) and comprise 2.37 and 1.22% of their respective polysomal RNA populations. Homologous poly(A)+ RNA-cDNA hybridizations revealed that greater than 95% of the mass of poly(A)+ RNAfree and poly(A)+ RNAbound contain nucleotide complexities of about 3.4 x 10(7) and 6.0 x 10(6), respectively. This represents about 20,000 and 5,000 poly(A)+ RNA species of average sizes. Heterologous hybridizations suggested that considerable overlap exists between poly(A)+ RNAfree and poly(A)+ RNAbound sequences that cannot be attributed to cross-contamination. This was confirmed by conducting heterologous reactions using kinetically enriched cDNA populations. Heterologous hybridizations involving poly(A)+ RNA derived from tightly bound polysomes and cDNAfree indicated tha most of the overlapping sequences are not contributed by loosely bound (high-salt releasable) polysomes. The ramifications of these findings are discussed.
mesh_terms: D000818:Animals; D001483:Base Sequence; D002458:Cell Fractionation; D002499:Centrifugation, Density Gradient; D004247:DNA; D008099:Liver / Q000648:ultrastructure; D009693:Nucleic Acid Hybridization; D011061:Poly A / Q000032:analysis* / Q000378:metabolism; D011132:Polyribosomes / Q000032:analysis* / Q000378:metabolism; D012333:RNA, Messenger / Q000032:analysis* / Q000378:metabolism; D051381:Rats
chemical_list: D012333:RNA, Messenger; D011061:Poly A; D004247:DNA