ZIP kinase identified as a novel myosin regulatory light chain kinase in HeLa cells

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Abstract
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 zipper‐interacting protein kinase (ZIPK) which mediates apoptosis [Kawai et al. (1998) Mol. Cell. Biol. 18, 1642–1651]. Here we found that HeLa ZIPK phosphorylated the regulatory light chain of myosin II (MRLC) at both serine 19 and threonine 18 in a Ca2+/calmodulin independent manner. Phosphorylation of myosin II by HeLa ZIPK resulted in activation of actin‐activated MgATPase activity of myosin II. HeLa ZIPK is the first non‐muscle MLCK that phosphorylates MRLC at two sites.