The pdx genetic marker adjacent to the chloramphenicol biosynthesis gene cluster in Streptomyces venezuelae ISP5230: functional characterization The GenBank accession number for the sequence reported in this paper is AF286159.

Abstract

The pdx-4 mutation in Streptomyces venezuelae ISP5230 confers a growth requirement for pyridoxal (pdx) and is a marker for the genetically mapped cluster of genes associated with chloramphenicol biosynthesis. A gene regulating salvage synthesis of vitamin B6 cofactors in S. venezuelae was cloned by transforming a pdx-4 mutant host with the plasmid vector pDQ101 carrying a library of wild-type genomic DNA fragments, and by selecting for complementation of the host's pdx requirement. However, the corresponding replicative plasmid could not be isolated. Southern hybridizations and transduction analysis indicated that the complementing plasmid had integrated into the chromosome ; after excision by a second crossover, the plasmid failed to propagate. To avoid loss of the recombinant vector, a pdxdependent Streptomyces lividans mutant, KAA1, with a phenotype matching that of S. venezuelae pdx-4, was isolated for use as the cloning host. Introduction of pIJ702 carrying an S. venezuelae genomic library into S. lividans KAA1, and selection of prototrophic transformants, led to the isolation of a stable recombinant vector containing a 25 kb S. venezuelae DNA fragment that complemented requirements for pdx in both S. venezuelae and S. lividans mutants. Sequence analysis of the cloned DNA located an intact ORF with a deduced amino acid sequence that, in its central and C-terminal regions resembled type-I aminotransferases. The N-terminal region of the cloned DNA fragment aligned closely with distinctive helix-turn-helix motifs found near the N termini of GntR family transcriptional regulators. The overall deduced amino acid sequence of the cloned DNA showed 73 % end-to-end identity to a putative GntR-type regulator cloned in cosmid 6D7 from the Streptomyces coelicolor A3(2) genome. This location is close to that of pdxA, the first pdx marker in S. coelicolor A3(2) identified and mapped genetically in Sir David Hopwood's laboratory. The S. venezuelae gene and S. coelicolor pdxA are postulated to be homologues regulating vitamin B6 coenzyme synthesis from pdx.

Positive transcriptional control of the pyridoxal phosphate biosynthesis genes pdxST by the MocR-type regulator PdxR of Corynebacterium glutamicum ATCC 13032

“…Disruption of the pdxR gene resulted in decreased expression of the pdxST genes and consequently in vitamin B 6 auxotrophy. In an earlier study, growth assays performed with Streptomyces venezuelae ISP 5230 showed similar results, as disruption of the so-called ORF1 caused a growth requirement for pyridoxal (Magarvey et al, 2001). The corresponding gene region was isolated by complementing the pdx-4 mutation of S. venezuelae, indicating a relationship between the expression of ORF1 and the availability of pyridoxal.…”

“…The corresponding gene region was isolated by complementing the pdx-4 mutation of S. venezuelae, indicating a relationship between the expression of ORF1 and the availability of pyridoxal. The protein encoded by ORF1 can be classified as a member of the MocR subfamily of GntR-type transcription regulators (Magarvey et al, 2001;Rigali et al, 2002). The PdxR protein from C. glutamicum was also grouped into this subfamily of regulatory proteins (Brune et al, 2005;McHardy et al, 2003).…”

Role of PdxR in the activation of vitamin B6 biosynthesis in Listeria monocytogenes

“…It has been shown that L. monocytogenes PdxR, a member of the MocR/GabR subfamily of the GntR family of transcriptional regulators, is an activator of the pdxST genes responsible for the de novo biosynthesis of PLP. A similar function in other bacteria was previously demonstrated or suggested for three more members of this subfamily, also called PdxR (Magarvey et al ., ; Jochmann et al ., ; El Qaidi et al ., ). It was shown here that L. monocytogenes PdxR responds directly to PLP, which serves as the only effector of the protein.…”

“…Three MocR/GabR‐type proteins from various bacteria, called PdxR proteins, have been shown to be required for the expression of genes of PLP biosynthesis (Magarvey et al ., ; Jochmann et al ., ; El Qaidi et al ., ). PLP is considered to be one of the most versatile cofactors and is essential, in addition to aminotransferases, for activity of numerous other metabolic enzymes, such as amino acid racemases, decarboxylases, aminomutases, and many others (Schneider et al ., ; Percudani and Peracchi, ).…”

GabR, a member of a novel protein family, regulates the utilization of γ‐aminobutyrate in Bacillus subtilis

“…It is known, however, that MocR is required for rhizopine utilization in Sinorhizobium meliloti (Rossbach et al. , 1994) and that PdxR is involved in the generation of pyridoxine cofactors in Streptomyces venezuelae (Magarvey et al. , 2001).…”