This a revised application to study a novel cDNA that may constitute a fourth subclass of the PLC family, termed PLC-alpha. Based on primary structural features, PLC-alpha is postulated to provide a direct link for regulation between signaling pathways utilizing heterotrimeric G proteins and Ras proteins. The overall goal of this project is to identify the molecular mechanisms by which PLC-alpha is regulated and activates downstream effectors. The specific aims are: 1) to examine functional and physical interactions between PLC-alpha and heterotrimeric G proteins, using transfection reconstitution approaches; and 2) to examine functional and physical interactions between PLC-alpha and monomeric G proteins, especially those of the Ras family, using transfection and reconstitution approaches. Structural motifs mediating the interactions of PLC-alpha with these regulatory proteins will be also delineated, using truncation and site-directed mutagenesis approaches.