[Molecular cloning of two Rab family proteins, S2 and S10]

Rab family proteins play important roles in vesicular transport. In mammals, more than 30 members of this family have been reported to date. I report here the cDNA cloning and analysis of the genomic organization of two Rab family proteins, S2 and S10. Mouse S2 cDNA was isolated from a spleen cDNA library. S2 encoded a novel Rab family protein with highest homology to human S10. Mouse S10 cDNA was isolated from a brain cDNA library. Mouse S10 was 92% homologous at the nucleotide level and 98% identical at the amino acid level to human S10. The amino acid sequences of mouse S2 and S10 were 55% identical, and these two proteins shared unique amino acid sequences at the effector domain. Mouse S2 and S10 genes were isolated from a genomic library. The genomic organization of these two genes was essentially identical, having two exons and a single intron. This structure was unique among reported rab family genes. These findings suggest that S2 and S10 would make a subgroup in Rab family. The phylogenetic tree made by a computer program was consistent to this idea. Northern blotting of mouse tissue RNAs indicated that S2 gene was expressed ubiquitously, whereas S10 gene was almost exclusively expressed in the brain. These results suggest that S2 and S10 play similar roles in vesicular transport, whereas S10 has more specialized function in the nervous system.