Characterization of 5'-terminal methylation of human alpha- and beta-globin mRNAs.

After incubating peripheral blood of various anemic individuals with [methyl-3H]methionine, 5'-terminal cap structures and the sequential methylation of human globin mRNAs were determined. Human alpha- and beta-globin mRNAs have the same methylated nucleotides at their 5' ends as the alpha- and beta-globin mRNAs of mouse and rabbit: m7G(5')ppp(5')[m6Am/Am]pCmp. The order of methyl group addition to human globin mRNA is also similar to that of mouse globin mRNA in that methylation of the 5'-terminal guanosine and the ribose of adenosine occurs earlier than that of the base of adenosine and the ribose of cytidine. Thus, both the cap structures and the order of methylation are conserved in the globin mRNAs of these species, suggesting that variation in the structure of the 5' terminus of globin mRNAs may alter the function of these molecules.