Analysis of a novel human ras GAP-like gene

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We have cloned a novel RasGAP-related molecule, nGAP, from human heart library. Among previously described RasGAPs, nGAP is most closely related to the synapse-specific RasGAP, SynGAP, and a Caenorhabditis elegans RasGAP, GAP-2. All these three molecules shere highly-conserved GAP-related domain in the middle of the molecules and predicted coiled-coil structure near their carboxyl termini.Tissue specificity of nGAP expression was examined by RT-PCR analysis to show the ubiquitous expression in all tissues examined.Expression of nGAP in Saccharomyces cerevisiae defective in one of two RasGAPs, Ira2, complemented the loss of the Ira2 function, indicating that nGAP functions as a RasGAP against yeast Ras proteins.RasGAP assay performed in vitro using recombinant GST-nGAP and recombinant GST-Ha-Ras did not show GAP activity, however. When nGAP was over-expressed in HeLa cell, serum-stimulated MAP kinase activation was not affected. These result raises the possibilities that nGAP targets other Ras-like low molecular weight G proteins than Ras or nGAP requires cirtain conditions or co-factors for the activity.Both FISH analysis on normal human metaphase chromosomes and radiation-hybrid analysis assigned the nGAP gene to the human chromosome 1q25, the locus that appears to contain a hereditary prostate cancer susceptible gene, HPC1. Considering the possibility that nGAP acts as RasGAP, this assignment raises a possibility that nGAP is the proposed HPC1.