Isolation of multiple mouse cDNAs with coding homology to Saccharomyces cerevisiae CDC25: identification of a region related to Bcr, Vav, Dbl and CDC24.

Abstract

In Saccharomyces cerevisiae, the product of the CDC25 gene is an essential Ras activator that appears to function by stimulating guanine nucleotide exchange on Ras. Using the ability of a mouse cDNA expression library to complement yeast cells lacking functional CDC25, Martegani et al. have identified a 1.7 kb partial cDNA from a gene, designated CDC25Mm, with homology to CDC25. We have now screened a mouse brain cDNA library to identify full‐length clones of CDC25Mm. This cloning has led to the isolation of six distinct full‐length cDNAs, each of which appear to be derived from the CDC25Mm gene, since their 3′ 2 kb appear to be identical and to encode the same 661 C‐terminal amino acids. Three cDNAs are predicted to encode protein products of 666 or 667 amino acids. The other three cDNAs encode products that are 836, 1120 and 1260 amino acids, respectively. A 241 amino acid region near the N‐terminus of the two largest products was found to have homology to a domain shared by Bcr, Vav, Dbl and CDC24. Polyclonal antibodies raised to a peptide encoded by all the cDNAs have identified at least two protein products in NIH3T3 fibroblasts. Their apparent molecular weights are 75 and 95 kDa, which correspond closely to those predicted to be encoded, respectively, by the two shorter classes of cDNAs. In NIH3T3, the 95 kDa form is much more abundant than the 75 kDa form, while PC‐12 pheochromocytoma cells contain relatively high levels of the 75 kDa form. We conclude that CDC25Mm is a complex gene whose protein products are regulated in a tissue‐specific manner.

rsc: a novel oncogene with structural and functional homology with the gene family of exchange factors for Ral

“…The hollow boxes represent the protein sequence of unrelated or less closely conserved regions of these proteins. The genes are as follows: ral/GDS ± mouse ral Guanine nucleotide Dissociation Stimulator (Albright et al, 1993); RGL ± mouse ral/GDS Like protein (Kikuchi et al, 1994); mCDC25h ± mouse CDC25 homologue (Cen and Lowy, 1992); Ras-GRF ± human ras Guanine nucleotide Releasing Factor (Shou et al, 1992); hCDC25h ± human CDC25 homologue (Wei and Broek, 1993); mSOS-1 ± mouse Son of Sevenless (Bowtell et al, 1992); CDC25 ± S. Cerevesiae guanine nucleotide dissociation stimulator for yeast Ras (Broek et al, 1987); ste6 ± S. pombe sterile 6, guanine nucleotide dissociation stimulator for yeast ras (Hughes et al, 1990) rsc oncogene homologous to Ral-GDS D D'Adamo et al truncated region of rgr present in rsc is, by itself, tumorigenic (Table 2). These results indicate that the tumorigenic potential of rsc is due either to the truncation or overexpression of rgr.…”

Sensitivity of wild type and mutant ras alleles to Ras specific exchange factors: Identification of factor specific requirements

“…Three classes of Ras speci®c exchange factors have so far been identi®ed in mammalian cells: Sos, GRF and GRP, of which Sos and GRF each have two members (Kaibuchi et al, 1991;Bowtell et al, 1992;Cen et al, 1992;Martegani et al, 1992;Shou et al, 1992;Chardin et al, 1993;Fam et al, 1997;Ebinu et al, 1998). The catalytic domain of GRF can activate all four Ras proteins in vitro (Orita et al, 1993;Leonardsen et al, 1996).…”

Basis for Signaling Specificity Difference between Sos and Ras-GRF Guanine Nucleotide Exchange Factors

“…Sos1 and Sos2 are highly similar GEFs that contain Grb2-binding domains, allowing them to be activated by cell-surface tyrosine kinases (2,12). Ras-GRF1 (also referred to as Cdc25 Mm ) (13,14) and Ras-GRF2 (15) are also highly similar GEFs that contain calmodulin-binding domains, allowing them to be activated by elevated calcium in cells (16,17). Ras-GRF1 can also be activated by phosphorylation (18 -20).…”