cDNA cloning of human hnRNP protein Al reveals the existence of multiple mRNA isoforms

Abstract

Protein Al is one of the major component of mammalian ribonucleoprotein particles (hnRNP). Human protein Al cDNA cloning and sequencing revealed the existence of at least two protein isoforms. Among the cDNAs examined, sequence differences were found both in the structural portion, leading to aminoacid changes (Tyr to Phe or Arg to Lys) and in the non ⁺ ranslated 3′-region where two T-stretches of different length were observed. Interestingly one of the aminoacid substitutions falls into a consensus sequence common to many RNA binding proteins. Northern blot analysis of poly A ⁺ RNAs from five human tissues revealed two mRNA forms of 1500 and 1900 n due to alternative polyadenylation. Analysis of genomic DNA showed at least 30 A1-specific sequences, some of which correspond to processed pseudogenes. These results suggest that protein Al is encoded by a multigene family.