Genetic organization and regulation of the xylose degradation genes in Streptomyces rubiginosus

Abstract

The xylose isomerase (xylA) and the xylulose kinase (xylB) genes from Streptomyces rubiginosus were isolated, and their nucleotide sequences were determined. The xylA and xylB genes encode proteins of 388 and 481 amino acids, respectively. These two genes are transcribed divergently from within a 114-nucleotide sequence separating the coding regions. Regulation of the xyl genes in S. rubiginosus was examined by fusing their promoters to the Pseudomonas putida catechol dioxygenase gene and integrating the fusions into the minicircle integration site on the S. rubiginosus chromosome. The expression of catechol dioxygenase was then measured under a variety of conditions. The results indicated that transcription of the xyl genes was induced by D-xylose and repressed by glucose. Data from quantitative S1 mapping were consistent with this conclusion and suggested that xylA had one and xylB had two transcription initiation sites. The transcription initiation site of xylA was 40 bp upstream of the coding region. The two transcription initiation sites of xylB were 20 and 41 bp 5' of its translation initiation codon. Under control of appropriate regulatory elements, the cloned xyl genes are capable of complementing either Escherichia coli xylose isomerase- or xylulose kinase-deficient strains. The deduced amino acid sequence of the S. rubiginosus xylA protein is highly homologous to sequences of other microbial xylose isomerases.

Cloning, sequencing and biochemical characterization of xylose isomerase from Thermoanaerobacterium saccharolyticum strain B6A-RI

“…thermosulfurigenes 4B (Lee et al, 1990b), Thermoanaerobacter ethanolicus 39E (formerly Clostridium thermohydrosulfuricum 39E) (Dekker et al, 1991b), E. coli (Schellenberg et al, 1984), B. subtilis (Wilhelm & Hollenberg, 1985), Streptomyces violaceoniger (Drocourt et al, 1988), Streptomyces rubiginosus (Wong et al, 1991) and Thermus thermophilus and the results are shown in Table 1 The length of the polypeptide chain encoded by the xylA gene in T. saccharolyticum strain BGA-RI was identical to that of T. thermosulfurigenes 4B (439 amino acid residues) and was similar to those of Thermoanaerobacter ethanolicus 39E (438 residues), and E. coli and B. subtilis (440 residues), whereas the enzymes from S. violaceoniger, Ampullariella and Arthrobacter have polypeptides which are shorter by 47 residues at the N-terminal. The deduced amino acid sequence of T. saccharolyticurn B6A-RI xylose isomerase exhibits very high homology to those from T. thermosulfurigenes 4B…”

Studies on the production of glucose isomerase by Bacillus licheniformis

“…The presence of D--xylose signifi cantly increased the enzyme productivity by Streptomyces spp. 19 . Replacement of D-xylose with glucose reduced GI production.…”

Restoration of a Defective Lactococcus lactis Xylose Isomerase

“…Isomerization and phosphorylation are catalyzed by D-xylose isomerase (XI; encoded by xylA) and D-xylulose kinase (encoded by xylB), respectively. In most cases, these genes are clustered into an operon (xyl operon) (14,22,24,33,39).…”

“…Group I includes XIs from genera such as Streptomyces (15,35,38,39), Actinoplanes (21,29,36), Thermus (9), and Arthrobacter (27,37). The average length of their polypeptide chains is 380 to 390 amino acids, and they have about 60% amino acid sequence identity, with the active-site residues being highly conserved.…”