>

(h) E. coli RNA Polymerase and E. coli Promoters

We also measured R_sequence for sites recognized by E. coli RNA polymerase. Hawley and McClure (1983) compiled data on 112 well characterized E. coli promoters. For these promoters aligned by the -35 and -10 regions and using the range given by Hawley and McClure, R_sequence is only 11.1 bits. There are two difficulties with this analysis. First, a variable gap was introduced between the two regions, which will increase the uncertainty Hsand decrease R_sequence substantially, perhaps as much as 2 bits (unpublished observation). The other difficulty is that a reasonable estimate for the number of promoters in E. coli does not exist, so R_frequency cannot be estimated. Nevertheless, promoters may be more frequent in E. coli (one per 500 bp) than is commonly assumed (see Discussion).