Mutations in the protein phosphatase 1 gene at 87B can differentially affect suppression of position-effect variegation and mitosis in Drosophila melanogaster.

Abstract

The suppressor of position effect variegation (PEV) locus Su-var(3)6 maps to 87B5-10. The breakpoints of deficiencies that define this interval have been placed on a 250-kb molecular map of the region. The locus is allelic to the ck19 complementation group previously shown to encode a type 1 serine-threonine protein phosphatase (PP1) catalytic subunit. When introduced into flies by P element-mediated transformation, a 5.8-kb genomic fragment carrying this gene overcomes the suppressor phenotype of Su-var(3)6(01) and recessive lethality of all mutations of the locus. Four of the mutant alleles at the locus show a broad correlation between high levels of suppression of PEV, a high frequency of aberrant mitosis and low PP1 activity in larval extracts. However, some alleles with low PP1 activity show weak suppression of PEV with a high frequency of abnormal mitosis, whereas others show strong suppression of PEV with normal mitosis. The basis for these discussed.

Protein phosphatase 1β is required for the maintenance of muscle attachments

“…A S66A/S67A non-phosphorylatable mutant of Mlc-2 [13] does not suppress any flw mutant phenotypes (data not shown). Though PP1α87B is the major isoform overall [2], it might be that PP1β9C is the only or major isoform present in muscles. The flw phenotype might then be due to a reduction in the overall PP1 activity in the muscle, rather than any isoform-specific role of PP1β9C.…”

“…We therefore measured the PP1 activity of muscle extracts from various PP1 mutants. The total PP1 activity of larvae homozygous for Pp1-87B 1 (also known as Su-var(3)6 01 [1,2]) is correspondingly reduced to about 20% of that of wild type and that of heterozygotes to about 50% of wild type. We found that the PP1 activity from extracts of larval body wall muscles of these genotypes was reduced by a similar proportion (Table 1), showing that PP1α87B is the major PP1 gene in these muscles.…”

KLP38B: A Mitotic Kinesin-related Protein That Binds PP1

“…Drosophila melanogaster has four genes encoding isoforms of PP1 (Dombrádi et al, 1990(Dombrádi et al, , 1993. Strong alleles of PP1 87B show PP1 activity reduced to ‫%02ف‬ of wild type in extracts of larvae and adults, indicating that this gene is the major isoform at these stages (Baksa et al, 1993). These mutants have a strong cell cycle phenotype: neuroblasts are delayed in mitosis and show aberrant spindle organization and hypercondensed chromatin.…”