6 exons, spread out over approximately 2,4 kb.

The Rac3 gene encompasses 6 exons on chromosome 17. Exon 1 encodes residues 1-12, exon 2 residues 13-36, exon 3 residues 37-75, exon 4 residues 76-96, exon 5 residues 97-149 and exon 6 residues 150-192.

Human Rac3 mRNA is a single species of around 1 kb. No splice variants have been reported. Factors that would regulate gene expression on a transcriptional level have not yet been reported.

No pseudogenes of Rac3 are reported in human.

The Rac3 gene encodes a single protein of 192 amino acid residues.

Rac3 is a small 21 kDa GTPase that acts as a molecular switch. In its active form, it is bound to GTP, whereas it is inactive in its GDP-bound form. Racs are controlled by guanidine activating proteins (GEFs) that exchange bound GDP for GTP and by GTPase activating proteins (GAPs) that promote GTP hydrolysis. Because of the hydrophobic isoprenyl moiety at the C-terminal end, it is associated with membranes. In the cytoplasm it associates with the chaperone RhoGDI.

Rac3 mRNA was reported in human cell lines including GM04155 (lymphoblastic leukemia), K562 (CML), 5838 (Ewing sarcoma), HL60 (promyelocytic leukemia) and DU4475 (breast cancer). Rac3 expression was reported using semi-quantitative RT/PCR in gastric tumor and adjacent normal tissue as well as gastric cancer cell lines. Expression of Rac3 using RT/PCR (38 cycles) was reported in human brain, liver, kidney and pancreas poly A RNA and also 19% of brain tumors expressed Rac3 mRNA. Rac3-specific polyclonal antibodies were used to show Rac3 protein in the brain (deep cerebellar nuclei and the pons) in 7 day old mice. Low level expression of mouse rac3 has been reported in bone-marrow-derived monocytes and in B-lineage lymphoblasts using standard and Real-Time RT/PCR. Expression of Rac3 is inferred because of the effect of siRNA knockdown in cell lines including HCT116 colon cancer, MDA-MB231 breast cancer, HeLa, and PC3 prostate cancer (Zhu et al., 2011). Real-time RT/PCR showed Rac3 mRNA in prostate cancer biopsy samples (Engers et al., 2007). Analysis of gene expression profiling datasets (Chang et al., 2005) in breast cancer samples showed Rac3 expression (Walker et al., 2011).

The Rac3 protein is located on endomembranes and cell membranes. Nuclear localization was also reported (Walker et al., 2011).

Rac proteins regulate a variety of functions including cytoskeletal organization, cell cycle, reactive oxygen species production, and vesicle trafficking. In its activity on reactive oxygen species production, Rac3 is able to activate Nox1, Nox2 and Nox3 (Miyano et al., 2009; Miyano and Sumimoto, 2012). Studies of null mutant Rac3 mice showed that Rac3 regulates cerebellar functions and in a mouse model plays a role in leukemia development caused by the Bcr/Abl oncogene. Point mutations (N26D, F37L, Y40C, N43D) were introduced into different critical residues of the effector domain of Rac3 and the effects of these were investigated on the ability of Rac3 to regulate membrane ruffles, c-jun activation and transformation. Transformation was assayed as the ability to cooperate with activated Raf in focus formation of NIH3T3 cells and the ability to promote growth of these cells in soft agar. Rac3 was found to negatively regulate autophagy in colon, breast and prostate cancer cell lines, since its knockdown stimulated LC3-II expression (Zhu et al., 2011). Different effects on migration are reported. Rac3 negatively regulates diapedesis of PC3 cells, since knockdown using siRNA increases migration of PC3 prostate cancer cells through a BMEC layer (Chatterjee et al., 2011). In contrast, overexpression of Rac3 in MCF7 breast cancer cells stimulates E2-induced migration (Walker et al., 2011).

Rac3 is most closely related to Rac1 and Rac2. On a nucleotide level human Rac3 has 77% identity with Rac1, 83% identity with Rac2 and 69% identity with RhoG. On an amino acid level, Rac3 and Rac1 differ in 14/192 residues (92% identical), whereas Rac3 and Rac2 differ in 22/192 residues (89% identical). Rac belongs to the extended Rho family of small G-proteins. Biochemically, Rac1 and Rac3 are closely related and have overlapping (Corbetta et al., 2009; Pennucci et al., 2011; Basso et al., 2011) as well as distinct functions. Rac3 differs from Rac1 in the presence of a residue in its C-terminal end, S151, which is A151 in Rac1 and mediates binding of Rac3 to ERα (Walker et al., 2011). Rac3 and Rac1 also differ in their effect on NIE-115 neuroblastoma cells, in which Rac3 induces cell rounding and Rac1 induces spreading (Hajdo-Milasinovic et al., 2007; Hajdo-Milasinovic et al., 2009).