title: Isolation of an operon involved in xylitol metabolism from a xylitol-utilizing Pantoea ananatis mutant.
abstract: An operon involved in cryptic xylitol metabolism of Pantoea ananatis was cloned by transposon tagging. A xylitol negative mutant with a transposon insertion in the xylitol 4-dehydrogenase gene (xdh) was isolated and genomic DNA around the transposon was sequenced. Consequently, six consecutive genes, xytB-G are located downstream of xdh in the same strand. These seven genes are cotranscribed as a single transcript in a P. ananatis xylitol-utilizing mutant, suggesting that they comprise an operon. In addition to xdh, xytF also encodes oxidoreductase that is a member of the short-chain dehydrogenase/reductase family. Recombinant Escherichia coli that heterologously expresses the Xdh protein converts xylitol to xylulose as expected. On the other hand, the recombinant XytF protein has activity with l-arabitol but not with xylitol. XytB, xytD and xytE have significant sequence similarities to genes encoding the substrate-binding, ATP-binding and permease subunits, respectively, of ATP-binding cassette transporters. Although the physiological role of the operon remains unknown, the operon appears to be involved in uptake and metabolism of a various sugar alcohols. A gene encoding a DeoR-type transcriptional regulator, xytR, is located upstream of the operon in the opposite strand and a single nucleotide substitution that could cause a nonsense mutation is present in the xytR gene of the xylitol-utilizing mutant. This result suggests that the product of xytR negatively controls expression of the operon like other DeoR regulators.
authors.affiliation: Fermentation Biotechnology Unit, National Center for Agricultural Utilization Research, Agricultural Research Service, U.S. Department of Agriculture, 1815 N. University st., Peoria, IL 61604, USA. sakaki@affrc.go.jp
authors.forename: Yoshikiyo
authors.initials: Y
authors.lastname: Sakakibara
authors.forename: Badal C
authors.initials: BC
authors.lastname: Saha
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D018389:Codon, Nonsense; D015964:Gene Expression Regulation, Bacterial; D015971:Gene Expression Regulation, Enzymologic; D008954:Models, Biological; D008957:Models, Genetic; D008969:Molecular Sequence Data; D009154:Mutation; D020636:Pantoea / Q000201:enzymology / Q000235:genetics*; D011485:Protein Binding; D011994:Recombinant Proteins / Q000737:chemistry; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D014993:Xylitol / Q000378:metabolism*
chemical_list: D018389:Codon, Nonsense; D011994:Recombinant Proteins; D014993:Xylitol