Genetic factors controllingwhitegene expression of the transposonAR4-24at a telomere inDrosophila melanogaster

The position effect of the AR 4-24 P[white, rosy] transposon was studied at cytological position 60F. Three copies of the transposon (within approximately 50-kb region) resulted in a spatially restricted pattern of white variegation. This pattern was modified by temperature and by removal of the Y chromosome, suggesting that it was due to classical heterochromatin-induced position effect variegation (PEV). In contrast with classical PEV, extra dose of the heterochromatin protein 1 (HP1) suppressed white variegation and one dose enhanced it. The effect of Pc-G, trx-G, and other PEV suppressors was also tested. It was found that E(Pc)1, TrlR85, and mutations of Su(z)2C relieve A(R) 4-24-silencing and z1 enhances it. To explain the results obtained with these modifiers, it is proposed that PEV and telomeric position effect can counteract each other at this particular cytological site.