Worm Breeder's Gazette 13(2): 41 (February 1, 1994)
These abstracts should not be cited in bibliographies. Material contained herein should be treated as personal communication and should be cited as such only with the consent of the author.
We have previously reported the characterization of the C. elegans p21 Ras-related Rho subfamily (WBG 12(5): 75). We have also shown that the nematode CDC42 homologue complements the yeast cdc42 -1temperature sensitive lethal mutation (Chen et al., J. Biol. Chem. 268: 13280-13285, 1993). The human breakpoint cluster region (Bcr) gene product is a member of a group of GTPase-activating proteins (GAP) which act exclusively on this subfamily. A cDNA was isolated (using the Bcr-related region of the genomic clone ZC21 as probe) from C. elegans (Chen et al., J. Biol. Chem. 269: 820-823, 1994). The cDNA clone designated as CeGAP is distributed over a 22 kb genomic region across 3 genomic clones ( F42H10 , C04D8 and ZC21 ) and therefore larger than the Bcr gene defined in the genome sequencing project. The 5 kb insert has an open reading frame of 1438 a. a. which contains a domain with sequence similarity to the COOH-terminal GAP region of Bcr and other known GAPs of the Rho subfamily. It also contains a 'pleckstrin homology' motif present in many signaling proteins including GAPs and nucleotide-exchange factors. However the absence of other domains in human Bcr (kinase and exchange factor) suggests that CeGAP represents a distinct molecule. The Bcr-like domain of CeGAP exhibited activity not only on members of the C. elegans and human Rho subfamily, but surprisingly also on C. elegans Ras protein ( let-60 ),human Ras and R ab3 A.CeGAP is therefore the first GAP acting on Ras-related proteins across different subfamilies. Together with the presence of the pleckstrin homology motif, our finding suggests a central and integrative role for CeGAP in a signalling pathway common to Ras and related proteins. Further analyses are underway; these include the isolation of the full length cDNA (as no stop codon is found in the 5' part of the cDNA) and production of antibody.
Additionally, the sequence of the nematode rhoGDI (GDP Dissociation Inhibitor) cDNA ( cm1 9 a7 )encoding 194 a.a. reveals 39% identity compared with the human counterpart (204 a.a.). To assess its activity which requires post-translationally processed substrates, the three nematode p21 Rho proteins (C eRac1 , CDC42 Ceand CeRhoA) are being expressed in S f9 insect cells via the baculovirus expression system.