FIG. 6.

Regulation of ifcR expression. (A) Regulatory region of the ifcR gene. The arrow indicates the transcription start site of the ifcR gene. The proposed ribosome-binding site is indicated by boldface type, and the putative −35 and −10 RNA polymerase recognition sequences are indicated by boldface type and underlining. A perfect palindromic sequence is underlined. (B) Primer extension analysis of ifcR performed with total RNA isolated from wild-type cells of S. frigidimarina and cells of ifcR mutant strain PSD106. +O₂, RNA from cells grown microaerobically on LB medium; −O₂+Fu, RNA from cells grown anaerobically with fumarate as the sole electron acceptor; −O₂+Fe, RNA from cells grown anaerobically with iron as the sole electron acceptor. Primer extension reactions were performed by using labeled oligonucleotide P1 (see Materials and Methods). Sequencing reactions were performed with the oligonucleotide that was used in the primer extension reactions. (C) Primer extension analysis of ifcR performed with total RNA isolated from wild-type cells of S. frigidimarina. +Fe, RNA from cells grown anaerobically with iron as the sole electron acceptor; Fe+Fu, RNA from cells grown anaerobically with fumarate and iron as electrons acceptors; Fe+Ni, RNA from cells grown anaerobically with iron and nitrate as electrons acceptors; +O₂, RNA from cells grown microaerobically on LB medium; +O₂ +Fe, RNA from cells grown microaerobically with ferric citrate.