Correction for Liu and Ochman, Stepwise formation of the bacterial flagellar system

EVOLUTION. For the article “Stepwise formation of the bacterial flagellar system,” by Renyi Liu and Howard Ochman, which appeared in issue 17, April 24, 2007, of Proc Natl Acad Sci USA (104:7116–7121; first published April 16, 2007; 10.1073/pnas.0700266104), the authors note that on page 7121, right column, line 4, the phrase “by using the Bl2seq program (with default options)” should instead read: “by using the Bl2seq program (with the ‘-F F’ option).” Additionally, in the Fig. 3 legend, line 3, the cutroff value 10⁻⁴ should instead appear as 9 × 10⁻⁴. Applying this cutoff yields a total of 70, not 24, hits of flagellar core proteins to nonflagellar proteins in the entire E. coli K-12 genome. These errors do not affect the conclusions of the article.