Frequency of His at the +3 position. The percentage of His at +3 was calculated from all unique peptides from 437 organisms. A high preference for His at +3 is observed for 16-stranded OMPs of β-Proteobacteria. Since there is a high number of 16-stranded OMPs in Burkholderia strains (see Additional file 1 and Additional file 2), they were also annotated in the plot.
Paramasivam et al. BMC Genomics 2012 13:510 doi:10.1186/1471-2164-13-510