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Appl. Environ. Microbiol., 08 1996, 2758-2766, Vol 62, No. 8
ZL Boynton, GN Bennett and FB Rudolph
The enzymes phosphotransacetylase (PTA) and acetate kinase (AK) catalyze
the conversion of acetyl coenzyme A to acetate in the fermentation of
Clostridium acetobutylicum. The acetate-producing step is an important
element in the acidogenic fermentation stage and generates ATP for
clostridial cell growth. The genes pta and ack, encoding PTA and AK,
respectively, were cloned and sequenced. Enzyme activity assays were
performed on cell extracts from Escherichia coli and C. acetobutylicum
harboring the subclone, and both AK and PTA activities were shown to be
elevated. DNA sequence analysis showed that the pta and ack genes are
adjacent in the clostridial chromosome, with pta upstream. The pta gene
encodes a protein of 333 amino acid residues with a calculated molecular
mass of 36.2 kDa, and ack encodes a polypeptide of 401 residues with a
molecular mass of 44.3 kDa. Primer extension analysis identified a single
transcriptional start site located 70 bp upstream of the start codon for
the pta gene, suggesting an operon arrangement for these tandem genes. The
results from overexpression of ack and pta in C. acetobutylicum showed that
the final ratios of acetate to other major products were higher and that
there was a greater proportion of two- versus four-carbon-derived products.
Copyright © 1996, American Society for Microbiology
Cloning, sequencing, and expression of genes encoding phosphotransacetylase and acetate kinase from Clostridium acetobutylicum ATCC 824
Department of Biochemistry and Cell Biology, Rice University, Houston, Texas 77005, USA.
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