Primary Structure of Protein Phosphatase 2A as Determined by Molecular Cloning: Implications for a Protein Phosphatase Gene Family
Post-translational modification of proteins is one of the major mechanisms employed in the control of cellular metabolism. Protein phosphorylation appears to be the most common regulatory form of post-translational modification. The phosphorylation state of proteins is controlled by the activity of protein kinases and phosphatases and changes in phosphorylation patterns, such as those caused by hormones and growth factors, must be mediated by changes in the activity of these enzymes. Much of the research effort in the field of protein phosphorylation has concentrated on the characterisation of protein kinases. Protein kinases can be classified into two broad groups: (a) those which modify tyrosine residues (Hunter and Cooper, 1985, 1986) and (b) those which modify either serine or threonine residues (Nairn et al, 1985; Beebe and Corbin, 1986; Kikkawa and Nishizuka, 1986). Cloning of cDNAs coding for receptor-tyrosine kinases and serine/threonine protein kinases has revealed extensive homology between the members of these two classes of enzymes (Hunter and Cooper, 1986). In addition, it has been found that multiple forms of some protein kinases (e.g. protein kinase C and cAMP-dependent protein kinase) exist (Coussens et al, 1986; Uhler et al, 1986a, 1986b; Showers and Maurer, 1986; Rao Adavani et al, 1987) which could explain some of the diverse properties attributed to these kinases (Kikkawa and Nishizuka, 1986; Beebe and Corbin, 1986).
KeywordsDeduce Amino Acid Sequence Protein Phosphatase Catalytic Subunit Myosin Light Chain Myosin Light Chain Kinase
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