Protein phosphatase 1 activity in Drosophila mutants with abnormalities in mitosis and chromosome condensation

A Drosophila gene encoding a protein phosphatase 1 (PP1) has been sequenced, and lethal mutations in this locus (87B) analysed. Two mutants (ck19e211 and ck19hs46), which disrupt mitosis, lack the 87B isoenzyme and express only approximately 20% of wild type PP1 activity. The promoter region of the gene is deleted in the ck19e211 mutant. A third mutant (ck19e078), which shows suppression of position effect variegation, but has little effect on mitosis, possesses approximately 35% of wild type PP1 activity. The results indicate that the PP1 87B isoenzyme is involved in regulation of chromosome condensation at interphase as well as mitosis.