Characterization of the insect specific putative kinase banshee in Drosophila melanogaster

Abstract

In differentiating cells, genes are silenced or transcribed through changes in chromatin organization. Active chromatin is known as euchromatin and repressive chromatin is known as heterochromatin. These active or repressive states are initiated and maintained by modifying residues of the core histone tails. Previous work has identified Su(var) and E(var) genes as modifiers of histone, with some roles in initiating heterochromatin or maintaining euchromatin, respectively. The gene bshe (CG8878) was identified in a forward genetic screen looking for recessive lethal Drosophila E(var) mutants. The amino acid sequence of this previously unstudied gene is predicted to be a protein kinase, based on its similarity to a known histone kinase. My research has begun to explore the function of bshe, and how it contributes to the heterochromatin/euchromatin balance. The predicted BSHE polypeptide has a kinase domain within the sequence. However, it also has a large interruption in the middle of the catalytic regions of the kinase domain, calling in to question whether it truly has kinase activity. Through phylogenetic analysis I characterize bshe to be an insect specific kinase of either an ancient or rapidly evolving clade. Predictions of the protein structure suggest that despite the large interruption, the main catalytic regions of the kinase domain are still in correct confirmation, suggesting that it still functions as a kinase. My observations of bshe mutant phenotypes show the majority of mutant hemizygotes to die by second instar larvae, with a maternal effect leading to earlier lethality. I completed an initial optimization of three antibodies, made against three polypeptides from BSHE, for Western blots and immunofluorescence. Initial observations show in syncytial embryos BSHE is localized to the cytoplasm.