SUBSTRATES FOR YEAST MITOCHONDRIAL CAMP-DEPENDENT PROTEIN-KINASE ACTIVITY

We showed that transcription of mitochondrial (mt) genes in Saccharomy ces cerevisiae is governed in part by cellular cAMP levels, and that s uch transcriptional control is mediated via cAMP-dependent protein kin ase (cAPK) activity. Here we use in vitro protein kinase assays with i ntact mitochondria from respiring cells to define protein substrates f or mt cAPK. Our data show that there are at least eight mt proteins ph osphorylated in a cAMP-dependent manner, ranging in M(r) from 96000 to 9500. Similar assays with organelles from an mtf1 mutant and its wild -type parent strain show no loss of any mt cAPK target proteins, sugge sting that Mtf1p (M(r)=40000), the mt RNA polymerase specificity facto r, does not require phosphorylation for activity. We further show, usi ng double mutants for TPK1, TPK2, and TPK3, which encode catalytic sub units of the mt cAPY that each of the eight mt substrate proteins is n ot phosphorylated equivalently by the individual catalytic subunits. ( C) 1995 Academic Press, Inc.