Long W tracts are over-represented in the Escherichia coli and Haemophilusinfluenzae genomes

The occurrence of DNA tracts of the three binary base combinations: R.Y, K. M and W;S has been mapped in the complete genomes of Haemophilus influenzae and Escherichia coli. A highly significant over-representation of W tracts is observed in both bacteria. The excess of W tracts is particularly strik ing in the 10% interceding regions. Subdivision of interceding regions into divergent (promoting), convergent (terminating) and sequential subregions shows that the excess of W tracts is most concentrated in the promoter regi ons. A particularly high excess of W tracts is observed in the first 200 ba ses 5' upstream of coding start sites. The data suggest that W tracts have a role in promoter function. A function as unwinding centers, analogous to the role of R.Y tracts in eukaryotes, is proposed. R.Y and K.M tracts are o nly modestly over-represented in the two bacteria.