Dosage compensation refers to the equalization of most X-linked gene products between males, which have one X chromosome and a single dose of X-linked genes, and females, which have two X's and two doses of such genes. In D. melanogaster, this equalization is achieved by assembling a multi-protein complex on the X chromosome in male somatic cells; the function of this complex is to enhance the transcription of X-linked genes in males. Complexes with a generally similar function have been identified in organisms as evolutionarily distant as yeast and humans; all appear to perform their function by remodeling chromatin. Therefore, the complete molecular definition of the mechanism used by flies to achieve X-chromosome dosage compensation will provide fundamental insights into the role that chromatin remodeling plays in the regulation of gene activity. Over the years, we have laid the necessary groundwork to understand the underlying regulatory mechanism of dosage compensation, at the molecular level and it is particularly satisfying to see that our hopes for this model system are being realized. Over the next grant period we propose the following specific experimental aims. (1) We will identify the remain components of the complex. To achieve this specific aim, we will supplement the genetic approaches that have relied on identifying gene products on the basis of sex-specific lethality with biochemical methods. (2) We will identify the sequence features that distinguish the X chromosome from the remainder of the genome. To date efforts, by others and ourselves have failed to reveal the features, which confer binding specificity to the dosage compensation complex. We will use a variety of molecular genetic and biochemical approaches to address this important aspect of the regulatory mechanism. (3) We will determine the nature of the mechanism underlying the function of the complex. This will involve a study of the interaction of the different components among themselves as well as with chromatin.
