Molecular cloning of a novel isotype of Mg²⁺-dependent protein phosphatase β (type-2Cβ) enriched in brain and heart

Two complementary DNA (cDNA) clones (pTK- 1 and-2) encoding two distinct isotypes of mouse Mg²⁺-dependent protein phosphatase β (MPPβ-1 and -2, respectively) were isolated from a melanocyte cDNA library. Although mouse pTK-1 is orthologous to the rat cDNA (JW5) reported previously [Wenk, J., Trompeter, H. I., Pettrich, K. G., Cohen, P. T. W., Campbell, D. G., and Mieskes, G. (1992) FEBS Lett. 297, 135-138], pTK-2 is a novel cDNA clone. It was strongly suggested that the pTK-1 and -2 cDNAs are splicing variants of a single pre-mRNA. The difference in the amino acid sequences between MPPβ-1 and -2 was observed only at the carboxyterminal regions. Both the recombinant MPPβ-1 and -2 expressed in Escherichia coli cells were immunoreactive to an anti-MPPβ antibody and exhibited Mg²⁺-dependent and okadaic acid-insensitive protein phosphatase activities with similar substrate specificities. Although the mRNA of MPPβ-1 was expressed ubiquitously in various mouse tissues, that of MPPβ-2 was expressed exclusively in brain and heart. These results suggest the difference in the physiological roles of these two enzyme isotypes.