Subject: 	FB Help Mailer: 995 Evolution of Rab gtpases genes
 comments:    Intraspecific Rabmony and interspecific Disrabmony
In D. melanogaster the Rab9D and Hmr genes, the latter of which is strongly implied in hybrid inviability, are separated by only 1 kb of genomic DNA. In D. ananassae, the ortholog (GF19340) of D. melanogaster Rab9D gene is located 1.8 kb from the Hmr ortholog. This strongly suggests that Rab9D and Hmr have remained tightly linked for more than 15 million years (corresponding to at least 200 million generations). In contrast with the six Rab9D paralogs present in D. melanogaster, the genome of D. ananassae contains a single Hmr linked Rab9D ortholog, just as D. yakuba and D. erecta do (as I reported last year in Advances in Genetics, Vol 58). RAB9D protein encoded by GF19340 in D. ananassae shows considerable divergence in more recent drosophila species, as it shares only about 60% and 45 % amino acid identities with RAB9D proteins from D. yakuba and D. mauritiana, respectively. This observation adds further evidence that the closely linked Rab9D and Hmr genes are evolving unusually fast, supporting the possibility of their additive role in causing hybrid incompatibilities. Noticeably, an AHGILLVYD motif from D. ananassae RAB9D protein is present in proteins encoded by Rab9D orthologs of D. erecta and D. yakuba, by the six Rab9D paralogs of D. melanogaster, but it is absent in the younger species D. simulans, D. sechellia and D. mauritiana. This is contrasted with the best conserved motif (VKLQIWDTAGEERFHS) of the RAB9D protein from D. ananassae, which is not present in proteins encoded by the six Rab9D paralogs of D. melanogaster, though it is found in RAB proteins from all drosophila species whose genome is available, as well as from most other eukaryotes including mammals.
    Pierre Hutter, PhD, FAMH
    Chef de l'Unité de Génétique Médicale
    Institut Central des Hôpitaux Valaisans
    Av. Grand-Champsec 86
    1951 Sion, Switzerland