In the pyruvate dehydrogenase complex (PDHC) of Zymomonas mobilis the L subunit of the pyruvate dehydrogenase (E1p) as well as the acetyltransferase (E2p) contain an N-terminal lipoyl domain. Both lipoyl domains were acetylated in vitro using 2-14 C-pyruvate as a substrate, demonstrating that both lipoyl domains can accept acetyl groups from the E1 component. As previously shown the structural genes (pdhAKL, pdhB, lpd) encoding the pyruvate dehydrogenase complex of Z. mobilis are located in two distinct gene clusters, pdhAKL and pdhB-orf2-lpd (U. . Analysis of pdh gene expression using lacZ fusions revealed that the DNA fragments upstream of pdhAK, pdhB and lpd each have promoter activities. These pdh promoter activities were 7^30-fold higher in Z. mobilis than in Escherichia coli. ß 1999 Federation of European Microbiological Societies. Published by Elsevier Science B.V. All rights reserved.