Guanine nucleotide-binding proteins (G proteins) are involved as modulators or transducers in various transmembrane signaling systems (PubMed:15240885, PubMed:16787920, PubMed:16705036, PubMed:27084452). Activates effector molecule RhoA by binding and activating RhoGEFs (ARHGEF1/p115RhoGEF, ARHGEF11/PDZ-RhoGEF and ARHGEF12/LARG) (PubMed:15240885, PubMed:12515866). GNA13-dependent Rho signaling subsequently regulates transcription factor AP-1 (activating protein-1) (By similarity). Promotes tumor cell invasion and metastasis by activating RhoA/ROCK signaling pathway (PubMed:16787920, PubMed:16705036, PubMed:27084452). Inhibits CDH1-mediated cell adhesion in process independent from Rho activation (PubMed:11976333). G proteins are composed of 3 units; alpha, beta and gamma (PubMed:12399457). The alpha chain contains the guanine nucleotide binding site (By similarity). Interacts with UBXD5 (PubMed:16202387). Interacts with HAX1 (PubMed:15339924). Interacts (in GTP-bound form) with PPP5C (via TPR repeats); activates PPP5C phosphatase activity and translocates PPP5C to the cell membrane. Interacts with RGS22 (PubMed:18703424). Interacts (in GTP-bound form) with ARHGEF1 (PubMed:10747909). Interacts (in GTP-bound form) with ARHGEF11 (via RGS domain) (PubMed:10026210). Interacts (in GTP-bound form) with ARHGEF12 (via RGS domain) (PubMed:11094164). Interacts with CTNND1 (PubMed:15240885). Interacts with GASL2L2 (PubMed:23994616). Identified by mass spectrometry in melanosome fractions from stage I to stage IV (PubMed:17081065). Detected in the cytoplasm of Leydig cells and in the seminiferous epithelium, including differentiating cells from the spermatogonia to mature spermatozoa stages (PubMed:18703424). In round spermatids, also present in the nuclei (PubMed:18703424). Expressed in testis, including in Leydig cells and in the seminiferous epithelium, in differentiating cells from the spermatogonia to mature spermatozoa stages and round spermatids (at protein level). Expressed in 99.2% of spermatozoa from healthy individuals, but only in 28.6% of macrocephalic spermatozoa from infertile patients (at protein level). Palmitoylation is critical for proper membrane localization and signaling. Phosphorylation on Thr-203 by PKA destabilizes the heterotrimer of alpha, beta and gamma, and inhibits Rho activation. Belongs to the G-alpha family. G(12) subfamily.