Small GTPase Rac1: Structure, localization, and expression of the human gene

Rac1 is a member of the Rho family of small GTPases involved in signal tran sduction pathways that control proliferation, adhesion, and migration of ce lls during embryonic development and invasiveness of tumor cells. Here we p resent the complete structure of the human RAC1 gene and characterize its e xpression. The gene comprises 7 exons over a length of 29 kb and is localiz ed to chromosome 7p22, The GC-rich gene promoter shows characteristics of a housekeeping gene and Northern blot studies revealed ubiquitous expression of two rad transcripts, 1.2 and 2.5 kb in size. The two transcripts are ex pressed in tissue-specific ratios, reflecting competition between two alter native polyadenylation sites. The RAC1 but not RAC2 gene contains an additi onal exon 3b that is included by alternative splicing into the variant Rac1 b, a constitutively active mutant which induces the formation of lamellipod ia in fibroblasts. These data indicate that the RAC1 gene encodes two signa ling GTPases. The gene structure reported here will enable studies on the r egulation of RAC1 expression during tumorigenesis and development. (C) 2000 Academic Press.