A novel group of multi-GAP-domain proteins.

The Rho GTPase-activating proteins (RhoGAPs) play an essential role in regulating various cellular processes. Rat tGAP1 is the first reported protein that has multiple GAP domains. It is exclusively expressed in male germ cells. However, tGAP1 does not possess GAP activities in vitro. No tGAP1 homology has been identified in other species. In this study, we searched the genomic databases and identified many genes whose protein products possess 2-4 GAP domains in rat, mouse and dog. These genes all showed sequence similarity to tGAP1. The rat tGAP gene loci all locate on chromosome 2 and are all expressed in testes in RT-PCR analysis. The mouse tGAP gene loci also clustered on chromosome 3 but RT-PCR analysis showed most are pseudogene loci. Multiple sequence alignment showed that many conserved residues of the "arginine finger" motif within the GAP domains of predicted tGAP proteins have mutated, suggesting that tGAP proteins do not possess GAP activity. We also elucidated the evolutionary relations among the rat tGAP genes. Based on the phylogenetic analysis data, we proposed that tGAP genes and Arhgap20 genes have a common ancestor.