Fig. 3. Recipient and donor RE GC content govern σ70 motif encoding within regulatory sequences.

a A simplified model that approximates the σ70 motif to an AT-rich multinomial sequence. The expected fraction of promoters with a motif match is plotted as a function of motif significance threshold for this simplified model. Each line represents a different recipient GC content, panels represent RE GC contents of 0.3, 0.5, and 0.7. Low GC promoters are more likely to contain σ70 motifs and GC-rich recipients are more likely to identify significant σ70 motifs. b The fraction of promoters with σ70 motif for a simulated regulatory library of random GC content follows similar trend observed in the simplified model represented in (a). Random promoters were generated with GC content in bins of 0.05 ranging from 0.1 to 0.8, 500 promoters for each bin, totaling 7500 promoters. c The fraction of promoters with σ70 motif in the library of regulatory sequences is consistent with the predictions from the simplified model (a) and random library (b).