ISOLATION OF AN ARABIDOPSIS-THALIANA CDNA BY COMPLEMENTATION OF A YEAST ABC1 DELETION MUTANT DEFICIENT IN COMPLEX-III RESPIRATORY ACTIVITY

The yeast Abc1 protein acts as a chaperone-like protein essential for the proper conformation and efficient functioning of the respiratory c omplex III. By functional complementation of a yeast abc1 mutant, we h ave identified an Arabidopsis thaliana cDNA that corresponds to a sing le copy gene and encodes a protein sharing 45% similarity with the yea st Abc1p protein. Cytochrome spectra and respiratory activity measurem ents have shown that the plant protein allows a partial restoration of the complex III activity. No major difference in the steady-state lev el of ABC1At mRNA was observed in various plant tissues, suggesting th at ABC1At is constitutively expressed in A. thaliana. Phylogenetic ana lysis revealed that the Abc1At protein belongs to a large family of pr oteins composed of two eukaryotic and one prokaryotic subgroups differ ing by their degree of similarity and probably by their function. (C) 1998 Elsevier Science B.V. All rights reserved.