A novel myosin light chain kinase (MLCK) cDNA was isolated from a HeLa cell
cDNA library. The deduced amino acid sequence was identical to that of a z
ipper-interacting protein kinase (ZIPK) which mediates apoptosis [Kawai et
al. (1998) Mol. Cell. Biol. 18, 1642-1651]. Here we found that HeLa ZIPK ph
osphorylated the regulatory light chain of myosin II (MRLC) at both serine
19 and threonine 18 in a Ca2+/calmodulin independent manner. Phosphorylatio
n of myosin II by HeLa ZIPK resulted in activation of actin-activated MgATP
ase activity of myosin II. HeLa ZIPK is the first non-muscle MLCK that phos
phorylates MRLC at two sites, (C) 1999 Federation of European Biochemical S
ocieties.