Alpha-subunit of geranylgeranyltransferase type III; required with β subunit Bet2p to transfer a geranylgeranyl group to mono-farnsylated Ykt6p, regulating membrane localization and its function in cell wall integrity and autophagy; involved in cell wall maintenance; functions in a regulatory pathway determining cell division readiness under stress; null is sensitive to osmotic stress and resistant to calcofluor white; structural and functional homolog of human GGTase-III α subunit PTAR1