Drosophila chromatin and transcription

In Drosophila transcription is differentially repressed by various aspects of chromatin, thought to represent distinct structural levels: the nucleosome core particle, the linker histone H1 and as yet undefined higher order structures. Heterochromatin serves as a paradigm for the latter level of organization, but maintenance of silencing at homeotic gene loci may also fall into this class. Recently GAGA transcription factor (GAF) was shown to counteract chromatin repression at all levels. The various effects of GAF could be explained by its ability to rearrange nucleosomal positions. Chromatin remodelling by GAF and other factors in vitro require activities that maintain a highly dynamic state of chromatin.