Stellate repeats: targets of silencing and modules causing cis-inactivation and trans-activation.

The mechanism of silencing of testis expressed X-linked Stellate repeats by homologous Y-linked Suppressor of Stellate [Su(Ste)] repeats localized in the crystal locus was studied. The double stranded RNA as a product of symmetrical transcription of Su(Ste) repeat and small interference Su(Ste) siRNA were revealed suggesting the mechanism of RNA interference (RNAi) for Stellate silencing. The relief of Stellate silencing as a result of impaired complementarity between the sequences of putative target Stellate transcripts and Su(Ste) repeats was shown. The role of RNAi mechanism in the silencing of heterochromatic retrotransposon GATE inserted in Stellate cluster was revealed. The studies of cis-effects of Stellate tandem repeats causing variegated expression of juxtaposed reporter genes were extended and the lacZ variegation in imaginal disc was shown. The exceptional case of a non-variegated expression of mini-white gene juxtaposed to Stellate repeats in a construct inserted into the 39C region was shown to be accompanied by trans-activation in homozygous state. Trans-activation effect was retained after transposition of this construct into heterochromatic environment in spite of strong variegation of a mini-white gene.