The Rhizobium etli sigma70 (SigA) factor recognizes a lax consensus promoter.
A collection of Rhizobium etli promoters was isolated from a genomic DNA library constructed in the promoter-trap vector pBBMCS53, by their ability to drive the expression of a gusA reporter gene. Thirty-seven clones were selected, and their transcriptional start-sites were determined. The upstream sequence of these 37 start-sites, and the sequences of seven previously identified promoters were compared. On the basis of sequence conservation and mutational analysis, a consensus sequence CTTGACN16-23TATNNT was obtained. In this consensus sequence, nine on of twelve bases are identical to the canonical Escherichia coli sigma70 promoter, however the R.etli promoters only contain 6.4 conserved bases on average. We show that the R.etli sigma factor SigA recognizes all R.etli promoters studied in this work, and that E.coli RpoD is incapable of recognizing them. The comparison of the predicted structure of SigA with the known structure of RpoD indicated that regions 2.4 and 4.2, responsible for promoter recognition, are different only by a single amino acid, whereas the region 1 of SigA contains 72 extra residues, suggesting that the differences contained in this region could be related to the lax promoter recognition of SigA.
Ramírez-Romero
Miguel A
MA
Programa de Genómica Evolutiva, Centro de Ciencias Genómicas, Universidad Nacional Autónoma de México, Apartado Postal 565-A, C.P 62210, Cuernavaca, Morelos, México.
Masulis
Irina
I
Cevallos
Miguel A
MA
González
Víctor
V
Dávila
Guillermo
G
D001419:Bacteria / Q000235:genetics; D001426:Bacterial Proteins / Q000378:metabolism*; D001483:Base Sequence; D001665:Binding Sites; D016384:Consensus Sequence; D004269:DNA, Bacterial / Q000737:chemistry; D012321:DNA-Directed RNA Polymerases / Q000378:metabolism*; D008969:Molecular Sequence Data; D016296:Mutagenesis; D011401:Promoter Regions, Genetic; D042163:Rhizobium etli / Q000235:genetics*; D016415:Sequence Alignment; D012808:Sigma Factor / Q000378:metabolism*; D013816:Thermodynamics; D024363:Transcription Initiation Site; D015533:Transcriptional Activation
D001426:Bacterial Proteins; D004269:DNA, Bacterial; D012808:Sigma Factor; C081775:RNA polymerase sigma 70; D012321:DNA-Directed RNA Polymerases