THE TRITHORAX-LIKE GENE ENCODES THE DROSOPHILA GAGA FACTOR

LITTLE is known about the way higher-order chromatin structure influen ces gene expression and chromosome topology in general. Genetic analys is in Drosophila has led to the discovery of two classes of genes, the regulators of homeotic genes and the modifiers of position-effect var iegation, which seem to be good candidates for encoding some of the fa ctors regulating chromatin functions(1,2). The Trithorax-like gene we describe here is required for the normal expression of the homeotic ge nes and is a modifier of position-effect variegation. We found that Tr ithorax-like encodes the GAGA factor which is involved in the formatio n of an accessible chromatin structure at promoter sequences(3). Our g enetic analysis suggests that the chromatin modelling function of the GAGA factor is not restricted to promoter regions.