Regulation of iron assimilation: nucleotide sequence analysis of an iron-regulated promoter from a fluorescent pseudomonad

An iron-regulated promoter was cloned on a 2.1 kb Bgl/II fragment from Pseudomonas sp. strain M114 and fused to the lacZ reporter gene. Iron-regulated lacZ expression from the resulting construct (pSP1) in strain M114 was mediated via the Fur-like repressor which also regulates siderophore production in this strain. A 390 by StuI-PstI internal fragment contained the necessary information for iron-regulated promoter expression. This fragment was sequenced and the initiation point for transcription was determined by primer extension analysis. The region directly upstream of the transcription start point contained no significant homology to known promoter consensus sequences. However the -16 to -25 by region contained homology to four other iron-regulated pseudomonad promoters. Deletion of bases downstream from the transcriptional start did not affect the iron-regulated expression of the promoter. The -37 and -43 by regions exhibited some homology to the 19 by Escherichia coli Fur-binding consensus sequence. When expressed in E. coli (via a cloned trans-acting factor from strain M114) lacZ expression from pSP1 was found to be regulated by iron. A region of > 77 bases but < 131 upstream from the transcriptional start was found to be necessary for promoter activity, further suggesting that a transcriptional activator may be required for expression.