COMPLEMENTATION OF ESCHERICHIA-COLI UNCD MUTANT STRAINS BY A CHIMERIC F-1-BETA SUBUNIT CONSTRUCTED FROM ESCHERICHIA-COLI AND SPINACH CHLOROPLAST F-1-BETA

Abstract

ATP-synthesizing F0F1-ATPases are complex enzymes consisting of at least eight different subunits. These subunits are conserved during evolution to a very variable degree ranging in pairwise comparison between, for example, Escherichia coli and spinach chloroplast from 20% to 66% identical residues. It was surprising to find that some of the less well conserved subunits like delta and epsilon could replace their E. coli counterparts, whereas the highly conserved beta subunit, which carries the active sits, in the E. coli enzyme could not be substituted by spinach chloroplast beta (Lill st al. (1993) Biochim. Biophys. Acta 1144, 278-284). We constructed a chimeric F-1-beta subunit consisting of spinach beta in which the 96 N-terminal amino acids were replaced by the respective residue sequence from E. coli beta. Whereas spinach beta did not complement E. coli uncD mutant strains, the chimeric beta subunit restored growth under conditions of oxidative phosphorylation.