Essential genes in proximal 3L heterochromatin of Drosophila melanogaster

We have further characterized essential loci within the centric heterochrom atin of the left arm of chromosome 3 (3L) of Drosophila melanogaster, using EMS, radiation and P element mutagenesis. We failed to find any new essent ial genes, a result that suggests a lower-than-average gene density in this region. Mutations affecting expression of the most proximal gene [lethal 1 , l1 or l(3)80Fj] act as dominant suppressors of Polycomb (Pc), behavior wh ich is consistent with a putative trithorax group (trx-G) gene. The third g ene to the left of the centromere [lethal 3, l3 or l(3)80Fh] is likely to c orrespond to verthandi (vtd), a known trx-G gene that plays a role in the r egulation of hedgehog (hh) expression and signalling. The intervening gene [lethal 2, l2 or l(3)80Fi] is required throughout development, and mutant a lleles have interesting phenotypes; in Various allelic combinations that su rvive, we observe fertility, bristle, wing, eye and cuticle defects.