J. Sojda et al., A rhizobial homolog of IHF stimulates transcription of dctA in Rhizobium leguminosarum but not in Sinorhizobium meliloti, GENE, 238(2), 1999, pp. 489-500
Sequence inspection identified several potential IHF binding sites adjacent
to the Rhizobium leguminosarum dctA promoter. IHF protected the -30 to -76
region from DNase I digestion, but systematic error in quantitative assays
suggested that this protein-DNA interaction is complex. IHF stimulated Dct
D-mediated transcriptional activation from the R. leguminosarum dctA promot
er both in vivo and in vitro. In contrast to R. leguminosarum dctA, the Sin
orhizobium meliloti dctA promoter region was found to have a much weaker ma
tch to the consensus IHF binding site and a low affinity for IHF. Moreover,
IHF had no effect on transcriptional activation from the S. meliloti dctA
promoter in vitro. A base substitution was introduced into the IHF binding
site of R. leguminosarum dctA that reduced the affinity of the promoter reg
ulatory region for IHF by similar to 30-fold and resulted in an eight-fold
decrease in transcriptional activation in both R. leguminosarum and S. meli
loti. These data suggest that both rhizobial species have an IHF homolog th
at stimulates DctD-mediated transcriptional activation from the Ii. legumin
osarum dctA promoter. Consistent with this hypothesis, a 12.5 kDa protein w
as identified from R. leguminosarum as a putative homolog of IHF subunit be
ta by immunoblotting and N-terminal sequence analysis. (C) 1999 Elsevier Sc
ience B.V. All rights reserved.