CLONING AND MESSENGER-RNA EXPRESSION OF HUMAN UNCONVENTIONAL MYOSIN-IC - A HOMOLOG OF AMEBOID MYOSINS-I WITH A SINGLE IQ MOTIF AND AN SH3 DOMAIN

The complete deduced amino acid sequence and mRNB expression of human unconventional myosin-IC (HuncM-IC) are described. Sequencing of overlapping cDNB clones reveals a message of 4666 nucleotides with a single open reading frame predicted to encode a 127 kDa protein of 1109 amino acids. HuncM-IC is composed of three discrete regions: a characteristic N-terminal myosin head with predicted actin and ATP-binding sites; a neck domain with an ''IQ motif'', predicted to bind a single light chain; and a C-terminal tail with a putative membrane-binding site. In addition, the tail contains an src-homology 3 domain. The presence of a single IQ motif and an src-homology 3 domain is reminiscent of ''long-tailed'' myosins-I from amoeboid organisms, a supposition confirmed by multiple sequence alignment. Northern blot analysis of human tissues shows that HuncM-IC is ubiquitously expressed, with the highest levels-in kidney prostate, colon, liver and ovary. The results show that ''amoeboid'' myosins-I are not restricted to amoeboid organisms, rather they are expressed in the metazoa as well.