Mutations in the nomad retroelement are modifiers of position-effect variegation in Drosophila melanogaster

Abstract

The E(var)63A ^P mutation of Drosophila melanogaster was isolated in a genetic screen for P-element induced enhancers of w ^m4 variegation. Remobilization of the P-element in E(var)63A ^P resulted in a loss of its ability to enhance position-effect variegation (PEV) of w ^m4, indicating that the P-element in this mutant resulted in the E(var) phenotype. An allele of E(var)63A ^P, Su(var)63A ^LTR was isolated following mobilization of the P-element. Su(var)63A ^LTR was demonstrated to suppress PEV associated with the variegating rearrangements w ^m4 and bw ^VDe2. The P-element insert in E(var)63A ^P was located in the cytogenetic region 63A by in-situ hybridization and was shown to be inserted into the 3'LTR of a copy of the nomad retroelement. Two additional P-element containing lines were identified that also contained P-inserts into copies of the nomad element and were Su(var)s. The level of nomad transcription in the E(var)63A ^P and Su(var)63A ^LTR mutations was shown to correlate with their effect on PEV, suggesting that the nomad element may be directly involved in the regulation of chromatin structure. Several models to explain the effect of mutations in the nomad element on PEV and retroelement expression are presented.