A 26,000-dalton peptide that contains both sites phosphorylated by cyclic AMP-dependent protein kinase has been isolated from turkey gizzard myosin light chain kinase. Following cleavage with S. aureus protease, it was shown that the first 19 residues from the amino-terminus of this peptide contained one of the two phosphorylated sites and had the following sequence: -lysine-alanine-phosphoserine-glycine-serine-serine-proline-threonine-serine -proline-isoleucine-asparagine-alanine-aspartic-acid-lysine-valine-glutamic acid-asparagine-glutamic acid- In addition, a second peptide, which presumable was isolated from the C-terminal portion of the 26,000-dalton paptide contained the following tentative sequence: -leucine-proline-phosphoserine-proline-valine-lysine-isoleucine- Presently, studies are under way to determine which of these two peptides is phosphorylated when calmodulin is bound to myosin light chain kinase and which is phosphorylated only when clamodulin is not bound to myosin light chain kinase. An enzyme that methylates DNA CpG sequences has been purified by Dr. Timothy Bestor (MIT, Cambridge, Massachusetts) and is being used as a potential substrate for a number of kinases. Myosin light chain kinase, protein kinase C and cylic AMP-dependent protein kinase are each being used in an effort to phosphorylate the DNA methylase.
