Enables 1-phosphatidylinositol-3-kinase regulator activity. Involved in regulation of phosphatidylinositol 3-kinase activity. Part of phosphatidylinositol 3-kinase complex. Human ortholog(s) of this gene implicated in ataxia with oculomotor apraxia type 3 and colon cancer. Orthologous to human PIK3R5 (phosphoinositide-3-kinase regulatory subunit 5). [provided by Alliance of Genome Resources, Apr 2022]