1887

Abstract

Summary: The enzymes for catabolism of the pentitols -arabinitol (Dal) and ribitol (Rbt) and the corresponding genes from and ) and and ) have been used intensively in experimental evolutionary studies. Four and four genes from the chromosome of 1033-5P14 were cloned and sequenced. These genes are clustered in two adjacent but divergently transcribed operons and separated by two convergently transcribed repressor genes, and . Each operon encodes an NAD-dependent pentose dehydrogenase ( and ), an ATP-dependent pentulose kinase ( and rbtK) and a pentose-specific ion symporter (dalT and rbtT). Although the biochemical reactions which they catalyse are highly similar, the enzymes showed interesting deviations. Thus, DalR (313 aa) and RbtR (270 aa) belong to different repressor families, and DalD (455 aa) and RbtD (248 aa), which are active as a monomer or as tetramers, respectively, belong to different dehydrogenase families. Of the two kinases (19.3% identity), DalK (487 aa) belongs to the subfamily of short -xylulokinases and RbtK (-ribulokinase; 535 aa) to the subfamily of long kinases. The repressor, dehydrogenase and kinase genes did not show extensive similarity beyond local motifs. This contrasts with the ion symporters (86.6% identity) and their genes (82.7% identity). Due to their unusually high similarity, parts of and have previously been claimed erroneously to correspond to ‘inverted repeats’ and possible remnants of a ‘metabolic transposon’ comprising the and genes. Other characteristic structures, e.g. a secondary attλ site and chi-like sites, as well as the conservation of this gene group in C are also discussed.

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/content/journal/micro/10.1099/00221287-144-6-1631
1998-06-01
2019-10-14
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http://instance.metastore.ingenta.com/content/journal/micro/10.1099/00221287-144-6-1631
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