EFFECTS OF THE MALELESS MUTATION ON X AND AUTOSOMAL GENE-EXPRESSION IN DROSOPHILA-MELANOGASTER

The mutational effect of the maleless (mle) gene in Drosophila has bee n reexamined. Earlier work had suggested that mle along with other mal e-lethal genes was responsible for hypertranscription of the X chromos ome in males to bring about dosage compensation. Prompted by studies o n dosage sensitive regulatory genes, we tested for effects of mle(ts) on the phenotypes of 16 X or autosomal mutations in adult escapers of lethality. In third instar larvae, prior to the major lethal phase of mle, we examined activities of 6 X or autosomally encoded enzymes, ste ady state mRNA levels of 15 X-linked or autosomal genes and transcript s from two large genomic segments derived from either the X or from ch romosome 2 and present in yeast artificial chromosomes. In contrast to the previously hypothesized role, we detected pronounced effects of m le on the expression of both X-linked and autosomal loci such that a l arge proportion of the tested genes were increased in expression, whil e only two X-linked loci were reduced. The most prevalent consequence was an increase of autosomal gene expression, which can explain previo usly observed reduced X:autosome transcription ratios. These observati ons suggest that if mle plays a role in the discrimination of the X an d the autosomes, it may do so by modification of the effects of dosage sensitive regulatory genes.