A small proteolipid called PMP1 is associated with yeast plasma membrane H(+)-ATPase (Navarre, C., Ghislain, M., Leterme, S., Ferroud, C., Dufour, J.-P., and Goffeau, A. (1992) J. Biol. Chem. 267, 6425-6428). We have identified a second Saccharomyces cerevisiae plasma membrane proteolipid gene by hybridization with a PMP1 probe. The sequence of the corresponding gene, called PMP2, is 92% identical to the PMP1 gene sequence. PMP2 encodes a 43-amino acid polypeptide that can be extracted from the membrane with chloroform/methanol. The two proteolipids differ at residue 21, which is an alanine in PMP1 and a serine in PMP2. The two PMP genes are similarly expressed in the wild-type strain, and no modification of the level of transcription of one PMP gene is detected in a strain deleted of the other. A regulatory function of the proteolipids is indicated by the observation that a strain lacking both PMP genes and no longer containing plasma membrane proteolipids displays a lower Vmax of the plasma membrane H(+)-ATPase activity.