ESSENTIAL LIGHT-CHAIN OF DROSOPHILA NONMUSCLE MYOSIN-II

We have cloned and sequenced a cDNA encoding the essential (alkaline) light chain of nonmuscle myosin from Drosophila melanogaster. The prot ein predicted from the cDNA matches partial amino acid sequence derive d from essential light chain protein that copurifies with native nonmu scle myosin heavy chain. This completes the sequence of the three myos in subunits, two of which have been shown genetically to be required f or morphogenesis and cytokinesis (the heavy chain encoded by zipper an d the regulatory light chain encoded by spaghetti squash). The essenti al light chain protein is 147 amino acids in length and is 53% identic al to human smooth muscle essential light chain. The sequence is consi stent with the presence of four helix-loop-helix domains seen in cryst allographic structures of the striated muscle myosin light chains and their close relative, calmodulin. We identified the most conserved res idues among essential light chain sequences from multiple phyla and pr esent their locations on the crystallographic structure of striated mu scle essential light chain. This highlights several conserved contacts among the myosin subunits that may be important for the structure and regulation of the myosin motor. The gene encoding Drosophila nonmuscl e essential light chain (Mlc-c) localizes to cytological position 5A6 and we discuss prospects for genetic analysis in this region.