THE PYRUVATE-DEHYDROGENASE COMPLEX OF THE CHEMOLITHOAUTOTROPHIC BACTERIUM THIOBACILLUS-FERROOXIDANS HAS AN UNUSUAL E2-E3 SUBUNIT FUSION

The genes encoding pyruvate dehydrogenase (PDH) of Thiobacillus ferroo xidans were previously located by cloning and sequence analysis of the region upstream of the genes encoding the citrate synthase and gamma- glutamylcysteine synthetase genes. The pdh genes of T. ferrooxidans we re able to complement an Escherichia coli aroP-lpd mutant for growth o n minimal medium lacking acetate, indicating that the T. ferrooxidans PDH complex was functional in E. coli. The predicted amino acid sequen ce of the T. ferrooxidans PDH complex contained three ORFs. The first ORF encoded a 36.7 kDa homologue of the PDH complex E1 alpha subunit, the second ORF a 37.4 kDa E1 beta subunit and the third ORF an unusual 102 kDa fusion of the E2 and E3 subunits. in spite of T. ferrooxidans being a Gram-negative bacterium, its PDH complex had more features in common with Gram-positive bacteria and eukaryotes.