TRANSCRIPTION OF THE REGION ENCODING THE FERRIC DICITRATE-TRANSPORT SYSTEM IN ESCHERICHIA-COLI - SIMILARITY BETWEEN PROMOTERS FOR FECA AND FOR EXTRACYTOPLASMIC FUNCTION SIGMA-FACTORS

We have analyzed the molecular mechanism of regulation of the ferric d icitrate transport system in Escherichia coli (Ec), by studying the tr anscription of the regulatory and structural genes under various envir onmental conditions, and by determining the location of their transcri ptional start points and promoter regions. We report here that the mai n species observed in Northern hybridization analyses were a 2.5-kb mR NA, encoded by the outer membrane protein receptor gene fecA, and a 1. 5-kb mRNA encoded by a region including the fecIR genes. The synthesis of the 2.5-kb fecA mRNA is regulated by both citrate and iron. Furthe rmore, transcription of fecA is dependent on the presence of FecI. The promoter region for the fecA mRNA, a likely site of action for FecI, is not related to the consensus promoter region for sigma(70) RNA poly merase in Ec K-12. However, it shows greatest similarity with promoter s of genes regulated by a new sub-family of sigma factors, i.e., the e xtracytoplasmic function (ECF) sigma factors, which are associated wit h the expression of genes involved in extracytoplasmic functions, sugg esting that FecI may act as a specialized sigma factor. We also show t hat the fecB,C,D,E transport genes are linked in operon fashion to fec A. Since the levels of the fecB,C,D,E RNAs are extremely low, as compa red to the level of fecA mRNA, it is likely that processing from the 3 ' end must occur and stop near the end of fecA where a hairpin structu re is located.