VERTEBRATES HAVE CONSERVED CAPPING PROTEIN ALPHA-ISOFORMS WITH SPECIFIC EXPRESSION PATTERNS

Capping protein (CP), a ubiquitous actin binding protein composed of a n alpha and a beta subunit, is important for actin assembly and fell m otility. Lower organisms have one gene and one isoform of each subunit . Chickens have two very similar alpha-subunit isoforms. To determine if vertebrates in general contain multiple alpha isoforms and If those alpha isoforms have conserved sequences, we isolated and analyzed alp ha subunit cDNA's in mice and humans, Both mice and humans also have t wo alpha isoforms. Phylogenetic analysis of the alpha isoform sequence s reveals that vertebrates have two highly conserved subfamilies, alph a 1 and alpha 2. The alpha 1 and alpha 2 subfamilies are very similar to each other but can be defined and distinguished from each other by a small number of key amino acid residues, In addition, 3' untranslate d cDNA sequences are conserved within the isoform subfamilies. To inve stigate the function of the alpha isoforms, we examined their expressi on In mouse cells and tissues. Endothelial cells contain only the alph a 2 isoform, and erythrocytes contain almost exclusively the alpha 1 i soform, Most tissues have both alpha 1 and alpha 2 isoforms but the ra tio of alpha 1:alpha 2 varies widely. Together, these findings support the hypothesis that the CP alpha isoforms have conserved, unique and essential roles in vertebrates. (C) 1997 Wiley-Liss, Inc.