Regulatory subunit of the PI3K gamma complex. Required for recruitment of the catalytic subunit to the plasma membrane via interaction with beta-gamma G protein dimers. Required for G protein-mediated activation of PIK3CG (By similarity). Greatly activated by G gamma proteins. Heterodimer of a catalytic subunit (PIK3CG/p120) and a regulatory (PIK3R5a/p101) subunit. Interacts with beta-gamma G protein dimers. Predominantly localized in the nucleus in absence of PIK3CG/p120. Colocalizes with PIK3CG/p120 in the cytoplasm. Translocated to the plasma membrane in a beta-gamma G protein-dependent manner. Ubiquitously expressed with high expression in fetal brain compared to adult brain. Abundant expression is observed in cerebellum, cerebral cortex, cerebral meninges, and vermis cerebelli. The heterodimerization region allows the binding to the catalytic subunit. The disease is caused by variants affecting the gene represented in this entry.