Effects of disrupting RNAP–GCRE interactions in vitro: analysis by MASTER. (A) Effect of sequence at TSS+1NT on %TSS for RNAP-βWT vs. RNAP-βD446A. Table lists the difference in %TSS (%TSS for RNAP-βWT − %TSS for RNAP-βD446A) at positions 6, 7, 8, or 9 for TSS-regions carrying G, A, C, or T at TSS+1NT. (B) Sequence preferences for TSS+1NT. Sequence logo (33) for TSS+1NT of above-threshold TSS (Left) and TSS that exhibited a large, ≥20%, reduction in %TSS in reactions performed with RNAP-βD446A vs. reactions performed with RNAP-βWT (Right).