[Trans-effect of modifiers on position-effect variegation in a set of euchromatin-heterochromatin rearrangements in Drosophila melanogaster].

The effects of suppressors of position-effect variegation were studied in a set of euchromatin-heterochromatin rearrangements of the X chromosome accompanied by inactivation of the gene wapl. The rearrangements differed from one another in the size of the heterochromatic block adjacent to euchromatin, with the euchromatin-heterochromatin border remaining unchanged. In one rearrangement (r20), the position effect caused by a small block of adjacent heterochromatin may be determined by its interaction with the neighboring main heterochromatic region of the X chromosome. Chromosome 3 (the RT chromosome) was found to have a strong suppressing effect on all rearrangements, irrespective of the amount of heterochromatin adjacent to euchromatin. Su-var(3)9, a known suppressor of the position-effect variegation, had a considerably weaker suppressing effect. The RT chromosome had the strongest suppressing effect on the rearrangement r20.