Fig 2.

Identification of a minimal nre promoter and its functional elements. (A) Upstream sequence of the nre operon in strain C089B. Underlined sequences indicate 5′-truncated variants −39 and −30. Bolded characters represent a proposed −35 element, −10 element, and the translational start site. (B) Map of the binary reporter plasmid used to test promoter truncations and mutations in either A. fabrum or E. coli. pKJ138 is nreA⁻, while pKJ140 is nreA⁺. (C) Reporter gene activity from truncations of the nre promoter region. A. fabrum cells harboring lacZ fusions with or without nreA were grown in the presence or absence of supplemental NiCl₂, and β-galactosidase activity was measured in Miller units (MU). Error bars represent standard deviation from the mean (n = 6). P values for t-tests of important comparisons are given. (D) Sequence alignment showing the −39 loss of function (LOF) and −39 gain of function (GOF) mutations (green). Underlined are putative −35 and −10 elements. Red denotes the putative operator sequence, and inverted arrows indicate the inverted repeats within this sequence. (E and F) Functional comparisons of promoter mutants shown in panel D were carried out in both A. fabrum (E) and E. coli (F). Data are formatted as in panel C. Error bars represent standard deviations from the mean (n = 6). P values for t-tests of important comparisons are given.