Role of multiple trans-acting regulators in modifying the effect of the retrotransposon copia on host gene expression in Drosophila.

We have examined the combinatorial effect of five trans-acting modifiers of white apricot, a copia retrotransposon-induced allele of the white eye-color gene. Quantitation of steady-state levels of copia transcripts for various modifier combinations at different developmental stages using northern analysis reveals nonadditivity and epistasis. Interestingly, extensive overexpression of copia transcripts caused by the modifier Ufo is altered up to twofold in level when Ufo is combined with either of the modifiers Mow or Wow. In general, double combinations do not elevate the level of copia transcripts more than twofold. The role of suppressor mutations in modifying the effect of transposable elements on host gene expression is discussed.