MAS37P, A NOVEL RECEPTOR SUBUNIT FOR PROTEIN IMPORT INTO MITOCHONDRIA

By screening a collection of Saccharomyces cerevisiae mutants temperat ure sensitive for growth on a nonfermentable carbon source, we have is olated a gene (termed MAS37) which encodes a novel receptor for protei n import into mitochondria. Mas37p is a 37-kD outer membrane protein w ith two putative membrane-spanning regions. Inactivation of the MAS37 gene renders cells temperature-sensitive for respiration-driven growth , inhibits import of precursors into isolated mitochondria, and is syn thetically lethal with a deletion of one of the genes encoding the imp ort receptors Mas70p or Mas20p. Inactivation of Mas37p with specific a ntibodies inhibits import of different precursors to different extents ; the precursor specificity of Mas37p resembles that of the previously described import receptor Mas70p. Mas70p and Mas37p form a 1:1 comple x in detergent extracts of mitochondria and overexpression of one prot ein enhances that of the other. We suggest that the Mas37p/Mas70p hete rodimer functions as a receptor for protein import into yeast mitochon dria and that the mitochondrial receptor system consists of hetero-oli gomeric subcomplexes with distinct binding activities, but overlapping precursor specificities.