MOLECULAR-GENETIC ANALYSIS OF DROSOPHILA ASH2, A MEMBER OF THE TRITHORAX GROUP REQUIRED FOR IMAGINAL DISC PATTERN-FORMATION

The ash2 gene is a member of the trithorax group of genes whose produc ts function to maintain active transcription of homeotic selector gene s. Mutations in ash2 cause the homeotic transformations expected for a gene in this group but, in addition, cause a variety of pattern forma tion defects that are not necessarily expected. The ash2 gene is locat ed in cytogenetic region 96A17-19 flanked by slowpoke and tolloid and is included in a cosmid that contains part of slowpoke. The ash2 trans cript is 2.0 kb and is present throughout development. The ASH2 protei n predicted from the nucleotide sequence of the open reading frame has a putative double zinc-finger domain, called a PHD finger, that is pr esent not only in the products of other trithorax group genes such as TRX and ASH1, but also in the product of a Polycomb group gene, PCL. P olyclonal antibodies directed against ASH2 detect the protein in imagi nal discs and in the nuclei of salivary gland and fat body cells. On i mmunoblots these affinity-purified antibodies detect a 70-kDa protein in larvae and a 53-kDa protein in pupae.