Differences in the distribution of poly(A) size classes in individual messenger RNAs from neuroblastoma cells

Neuroblastoma polysomal mRNAs have been fractionated by a combination of oligo(dT)-cellulose and Millipore filter techniques into four classes, each containing a different average length of poly(A). These classes are present in mRNAs isolated using different extraction techniques and they probably represent the steady state mRNA distribution in neuroblastoma cells. Quantitation of the biological activity of each fraction in a wheat germ translation system shows that 32% of the mRNAs contain no oligo(A)s longer than 6; 4% have poly(A)s between 6 and 20 nucleotides, 22% have between 20 and 50 nucleotides, and 42% have greater than 50 nucleotides. Two-dimensional gel electrophoresis of the proteins synthesized by the unfractionated and fractionated mRNAs showed there was no mRNA degradation during the fractionation procedures. Analysis of the most abundant peptides synthesized by each RNA fraction shows that most mRNAs are found in each of the four populations. However, the distribution of some individual mRNAs varies widely. The α- and β-tubulin mRNAs are examples of those which are more abundant in the population with long poly(A)s. In contrast, a significant proportion of the mRNAs coding for actin and the R ₁ and R ₂ cAMP-binding proteins are nonadenylated. The histone mRNAs are unique in that they are more abundant in the non-adenylated mRNAs than in the mRNAs containing short stretches of poly(A). These results are consistent with a model wherein the poly(A) termini in some mRNA species are more rapidly cleaved than in others.