Mutants affecting position-effect heterochromatinization in Drosophila melanogaster.

The dominant suppressor Su(var)b101 and the dominant enhancer En(var)c101 were found to affect significantly white variegation in a strongly variegating line of the Wm4 chromosome (Wm4h) which has been used as standard rearrangement for a genetic dissection of position-effect variegation (Reuter and Wolff, 1981). Both mutations were also shown to affect position-effect heterochromatisation in T (1 ; 4)Wm258-21 and variegation in all the rearrangements tested (white, brown, scute and bobbed variegation). These results suggest that the genes identified encode functions essential for the manifestation of gene inactivation in position-effect rearrangements. It seems also reasonable to assume that in all the rearrangements tested identical heterochromatisation processes lead to inactivation of the genes whose phenotype is variegated.