The cAMP receptor protein SYCRP1 in cyanobacterium Synechocystis sp. PCC 6803 is a regulatory protein that binds to the consensus DNA sequence (5′-AAATGTGATCTAGATCACATTT-3′) for the cAMP receptor protein CRP in Escherichia coli. Here we examined the effects of systematic single base-pair substitutions at positions 4-8 (TGTGA) of the consensus sequence on the specific binding of SYCRP1. The consensus sequence exhibited the highest affinity, and the effects of base-pair substitutions at positions 5 and 7 were the most deleterious. The result is similar to that previously reported for CRP, whereas there were differences between SYCRP1 and CRP in the rank order of affinity for each substitution.
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