Analysis of the functional specificity of RS domains in vivo.

A number of splicing factors contain extensive regions that are rich in arginine and serine (RS domains). These domains are thought to facilitate 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. The RS domain of dU2AF50 functioned efficiently, while that of the dSRp55 protein did not. Moreover, we find similar differences in the ability of RS domains to direct fusion proteins to discrete subnuclear sites at which TRA-2 associates with spermatocyte chromosomes. These results indicate that RS domains are not all functionally equivalent in vivo.