Dissection of recognition determinants of Escherichia coli σ³² suggests a composite -10 region with an 'extended -10' motif and a core -10 element

• Published in: Molecular microbiology 2009-05, Vol.72 (4), p.815-829
• Main Authors: Koo, Byoung-Mo, Rhodius, Virgil A, Campbell, Elizabeth A, Gross, Carol A
• Format: Article
• Language: English
• Subjects: Bacteriology; Biological and medical sciences; Fundamental and applied biological sciences. Psychology; Microbiology; Miscellaneous
• ISSN: 0950-382X; 1365-2958
• DOI: 10.1111/j.1365-2958.2009.06690.x

σ³² controls expression of heat shock genes in Escherichia coli and is widely distributed in proteobacteria. The distinguishing feature of σ³² promoters is a long -10 region (CCCCATNT) whose tetra-C motif is important for promoter activity. Using alanine-scanning mutagenesis of σ³² and in vivo and in vitro assays, we identified promoter recognition determinants of this motif. The most downstream C (-13) is part of the -10 motif; our work confirms and extends recognition determinants of -13C. Most importantly, our work suggests that the two upstream Cs (-16, -15) constitute an 'extended -10' recognition motif that is recognized by K130, a residue universally conserved in β- and γ-proteobacteria. This residue is located in the α-helix of σDomain 3 that mediates recognition of the extended -10 promoter motif in other σs. K130 is not conserved in α- and δ-/ε-proteobacteria and we found that σ³² from the α-proteobacterium Caulobacter crescentus does not need the extended -10 motif for high promoter activity. This result supports the idea that K130 mediates extended -10 recognition. σ³² is the first Group 3 σ shown to use the 'extended -10' recognition motif.