Human profilin. Molecular cloning, sequence comparison, and chromosomal analysis.

Profilin is an ubiquitous 12-15-kDa actin monomer-binding protein, the amino acid sequence of which was previously reported for the cow and Acanthamoeba. In the latter species, two isoforms of profilin have been identified. We have isolated full-length profilin cDNA clones from a human HepG2 library. All clones have the same nucleotide sequence, and Northern blot and RNase protection analyses of human tissues indicate that all tissues have the same approximately 850 base message, and provide no evidence of alternative message splicing. This result strongly implies a single profilin isoform in human cells, although differential post-translational modifications have not been excluded. Northern blot analysis extends the tissue distribution of profilin to include epithelial, muscle, and renal tissues. Comparison of the predicted human profilin amino acid sequence with that of published bovine profilin indicates 90% identity with a single 3-residue deletion in the human sequence. Southern blot analysis of somatic cell hybrid DNA indicates at least four dispersed genetic loci in the human genome hybridize with the profilin cDNA as well as untranslated region fragments, suggesting several of these loci represent pseudogenes of recent evolutionary origin. In addition, 5' and 3' untranslated regions are conserved between humans and rodents, implying a functional role for these regions of the profilin gene.