HETEROCHROMATIC TRANS-INACTIVATION OF DROSOPHILA WHITE TRANSGENES

Position effect variegation of most Drosophila melanogaster genes, inc luding the white eye pigment gene, is recessive. We find that this is not always the case for white transgenes. Three examples are described in which a lesion causing variegation is capable of silencing the whi te transgene on the paired homologue (trans-inactivation). These examp les include two different transgene constructs inserted at three disti nct genomic locations. The lesions that cause variegation of white min imally disrupt the linear order of genes on the chromosomes, permittin g close homologous pairing. At one of these sites, trans-inactivation has also been extended to include a vital gene in the vicinity of the white transgene insertion. These findings suggest that many Drosophila genes, in many positions in the genome, can sense the heterochromatic state of a paired homologue.