Run-length distributions. Symbols show the number of matches between E. coli and several sets of genomes as a function of the length of the exact amino-acid match. Each match is counted only once, at the value of its maximal extension. For E. coli compared to B. subtilis (red crosses), the distribution is extended down to k = 3, and an exponential fit is shown as a solid red line. For k > 9, run-length distributions are shown for E. coli compared to a set of 22 other representative bacteria (green x), a set of 35 gamma proteobacteria (blue asterisks), and 17 representative enteric bacteria (cyan boxes).