A Drosophila gene encoding a protein phosphatase 1(PPI) has been sequenced, and lethal mutations in this locus (87B) analysed. Two mutants (ck19 e211 and ck19 hs46), which disrupt mitosis, lack the 87B isoenzyme and express only ∼20% of wild type PPI activity. The Promoter region of the gene is deleted in the ck19 e11 mutant. A third mutant (ck19 e078), which shows suppression of position effect variegation, but has little effect on mitosis, possesses ∼35% of wild type PPI activity. The results indicate that the PPI 87B isoenzyme is involved in regulation of chromosome condensation at interphase as well as mitosis.
