The pqrAB operon is responsible for paraquat resistance in Streptomyces coelicolor.
Paraquat (methyl viologen)-resistant mutants of Streptomyces coelicolor A3(2) that grew and sporulated normally in the presence of paraquat were isolated. Based on the positions of the mutant loci in the genetic map, we isolated the pqr (paraquat resistance) gene whose mutation (pqr501) caused a dominant paraquat-resistant phenotype. The pqr locus consists of two genes (pqrA and pqrB) that form a transcription unit. The pqrA gene encodes a protein with a TetR-like DNA-binding motif, and the pqrB gene encodes a putative efflux pump of the major facilitator superfamily. The pqr501 mutation was a base substitution changing arginine-18 to glutamine (R18Q) near the helix-turn-helix motif in PqrA. A pqrA null mutant exhibited similar paraquat resistance, and an increase in the amount of pqrA promoter-driven transcripts of about eightfold was observed for the pqrA501 mutant. These results suggest that PqrA is a negative regulator of its own operon. Deletion of the pqrAB operon caused cells to be very sensitive to paraquat, consistent with the prediction that PqrB may function as a paraquat-efflux pump. Purified PqrA protein specifically bound to the pqrA promoter region, whereas mutant R18Q protein did not, indicating that PqrA is a direct autoregulator of its own operon.
Cho
You-Hee
YH
Department of Life Science, Sogang University, Seoul 121-742, Korea.
Kim
Eun-Ja
EJ
Chung
Hye-Jung
HJ
Choi
Jae-Hyun
JH
Chater
Keith F
KF
Ahn
Bo-Eun
BE
Shin
Jung-Ho
JH
Roe
Jung-Hye
JH
D000595:Amino Acid Sequence; D001483:Base Sequence; D003001:Cloning, Molecular; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D024881:Drug Resistance, Bacterial / Q000235:genetics; D005798:Genes, Bacterial; D006540:Herbicides / Q000494:pharmacology*; D026901:Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D009154:Mutation; D009876:Operon; D010269:Paraquat / Q000494:pharmacology*; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism; D016415:Sequence Alignment; D013302:Streptomyces / Q000187:drug effects / Q000235:genetics*
D004268:DNA-Binding Proteins; D006540:Herbicides; D026901:Membrane Transport Proteins; D012097:Repressor Proteins; D010269:Paraquat