To define the role of the auto-inhibitory region of protein kinase C (PKC), Arg22-Lys23-Gly24-Ala25-Leu26-Arg27, site-directed mutations were introduced into the basic residues. Three mutants, PKCAla22,23, PKCAla27 and PKCAla22,23,27, apparently fell into two distinct types with regard to their biochemical properties and biological activities, as judged by the enhancement of a c-fos promoter in Jurkat cells and by the initiation of germinal vesicle breakdown (GVBD) in Xenopus laevis oocytes. (i) PKCAlu22,23 and PKCAla27 had activators independent in vitro kinase activity, high phosphorylation levels in vivo, and localized in both cytosolic and particulate fractions. These mutants were not fully biologically active. (ii) PKCAla22,23,27 had a low phosphorylation level in vivo, was found predominantly in the particulate fraction and was the most biologically active. These results suggest that basic residues in the auto-inhibitory domain account for the regulation of kinase activity and the cytosolic retention of PKC. The particulate association or the cytosolic clearance of PKC may facilitate signal transduction in the cell.
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