Molecular weights, poly(A)--content, and partial separation of chick globin mRNAs

Poly(A)-containing 9S RNA from chick reticulocytes was electrophoresed on formamide-polyacrylamide gels. The molecular weight was determined to be 211 000 +/- 10 000 daltons. The RNA was separated into three different fractions with respect to molecular weight. These RNAs were translated in a wheat germ cell-free system. The lower molecular weight RNA directed up to 95% alpha-chain synthesis, compared to 60% for the higher molecular weight RNA. This was accompanied by a relative increase for beta-chain synthesis with increasing molecular weight. It could also be shown by hybridization with labelled poly(U) that the average poly(A) length decreased from about 83 nucleotides for fraction I to 36 nucleotides for fraction III. Our results suggest that fractionation of avian 9 S globin mRNA by electrophoresis on formamide-polyacrylamide gels is dependent upon two parameters, namely differences in the lengths of the non-poly(A)-containing portion of the alpha and beta mRNAs and differences in the poly(A) lengths.