ROLE OF PROTEIN PHOSPHATASE 2A IN DROSOPHILA DEVELOPMENT

The molecular cloning of protein phosphatase 2A subunits from Drosophi la has provided insights into the role this enzyme plays in developmen tal processes and in cell cycle regulation. The trimeric holoenzyme co ntaining the catalytic, 65-kDa and 55-kDa regulatory subunits appears to be preferentially expressed in proliferative organs such as the gon ads, in the developing nervous system and in early syncytial embryos. Analysis of mutant flies affected in the expression of the 55-kDa regu latory subunit suggests that the holoenzyme containing this subunit pl ays a pivotal role in cell cycle regulation and cell fate determinatio n. The severity of the mutant phenotype correlates with a decrease in 55-kDa subunit protein levels and reduced protein phosphatase activity towards p34(cdc2) phosphorylated proteins. The data support the idea that the 'variable' subunits of protein phosphatase 2A holoenzymes pla y a critical rob in directing substrate specificity.