ANALYSIS OF THE FUNCTIONAL SPECIFICITY OF RS DOMAINS IN-VIVO

A number of splicing factors contain extensive regions that are rich i n arginine and serine (RS domains). These domains are thought to facil itate protein-protein interactions that are critical in the regulation of alternative splicing. Using a domain swap strategy, we have tested the ability of RS domains from several proteins to substitute in vivo for an essential RS domain in the Drosophila splicing regulator TRA-2 . By several criteria, RS domains were found to vary significantly in their ability to support the splicing regulation functions of TRA-2. T he RS domain of dU2AF(50) functioned efficiently; while that of the dS Rp55 protein did not. Moreover, we find similar differences in the abi lity of RS domains to direct fusion proteins to discrete subnuclear si tes at which TRA-2 associates with spermatocyte chromosomes. These res ults indicate that RS domains are not all functionally equivalent in v ivo.