Rab27a is a member of a large family of Ras-related small GTPases. The protein is membrane-bound and may be involved in protein transport and small GTPase mediated signal transduction. Recent studies suggest that Rab27a is associated with melanosomes in pigmented cells and regulates melanosome transport via its interaction with actin-based cellular motors such as myosin Va and myosin VIIa. RAB27A is also required for regulated secretion in cytotoxic T lymphocytes. Rab27a is implicated in several diseases,including Griscelli syndrome,choroideremia,and the Hermansky-Pudlak syndrome mouse model,gunmetal.