Phosphorylation at Serines 216 and 221 Is Important for Drosophila HeT-A Gag Protein Stability

Abstract

Telomeres from Drosophila appear to be very different from those of other organisms – in size and the mechanism of their maintenance. In the absence of the enzyme telomerase, Drosophila telomeres are maintained by retrotransposition of three elements, HeT-A, TART, and TAHRE, but details of their transposition mechanisms are not known. Here we characterized some biochemical characteristics of the HeT-A Gag protein encoded by the HeT-A element to understand this mechanism. The HeT-A Gag protein when overexpressed in S2 cells was localized to the nucleus but was resistant to high salt, detergents and nuclease extraction treatments. Analysis of the HeT-A Gag protein by tandem mass spectrophotometry revealed that serines 216 and 221 are phosphorylated. Substituting these serines with alanine or aspartic acid by site-directed mutagenesis did not result in any changes in HeT-A Gag translocation across the nucleus, suggesting that phosphorylation of these sites is not associated with HeT-A Gag translocation, but time course experiments showed that these phosphorylation sites are important for Gag-protein stability.

Loss of telomere silencing is accompanied by dysfunction of Polo kinase and centrosomes during Drosophila oogenesis and early development

“…The mechanism of selective interaction of mitotic kinases with HeT-A Gag cytoplasmic granules is unclear. HeT-A Gag is phosphorylated, which is important for the protein stability [78]. It has been reported that Cdk1 activity produces the docking sites for Polo recruitment to its targets [79][80][81].…”