AN X-CHROMOSOME-LINKED GENE ENCODING A PROTEIN WITH CHARACTERISTICS OF A RHOGAP PREDOMINANTLY EXPRESSED HEMATOPOIETIC-CELLS

An increasingly large number of proteins involved in signal transducti on have been identified in recent years and shown to control different steps of cell survival, proliferation, and differentiation. Among the genes recently identified at the tip of the long arm of the human X c hromosome, a novel gene, C1, encodes a protein that appears to represe nt a newly discovered member of the group of signaling proteins involv ed in regulation of the small GTP binding proteins of the ras superfam ily. The protein encoded by CI, p115, is synthesized predominantly in cells of hematopoietic origin, It is characterized by two regions of s imilarity to motifs present in known proteins: GAP and SH3 homologous regions, Its localization in a narrow cytoplasmic region just below th e plasma membrane and its inhibitory effect on stress fiber organizati on indicate that p115 may down regulate rho-like GTPases in hematopoie tic cells.