Molecular weight determinations on the alpha-globin and beta-globin mRNAs.

The globin mRNAs containing between 30 and 40 polyadenylate residues can be separated from thos mRNAs containing longer poly(A) regions by Millipore filter binding. The molecular weights of the alpha-and beta-globin mRNAs containing this size class of poly(A) have beed determined by lectrophoresis on 3.7% polyacrylamide gels in the presence of 99% formamide. Because the number of adenylic acid residues in these mRNAs is known, the number of non-poly(A) nucleotides can be accurately calculated. The molecular weight of the beta-globin mRNA is 235 000 +/- 28 000 (736 +/- 88 nucleotides) and that of the alpha-globin mRNA is 208 900 +/- 43 870 (653 +/- 78 nucleotides). By subtracting the number of nucleotides in the coding and poly(A) regions, the number of non-coding nucleotides in the beta-globin mRNA were calculated to be 261, 69 more than the 193 present in the alpha-globin mRNA. Comparison of size estimates of newly synthesized globin mRNAs containing longer average lengths of poly(A) shhowed that there is no comparable processin of the 5' termini of the alpha-and beta-globin mRNAs concomitant with the stepwise degradation of the poly(A) regions which occur as the mRNAs mature.