Transcription Activation Mediated by a Cyclic AMP Receptor Protein from Thermus thermophilus HB8

The extremely thermophilic bacteriumThermus thermophilus HB8, which belongs to the phylumDeinococcus -Thermus , has an open reading frame encoding a protein belonging to the cyclic AMP (cAMP) receptor protein (CRP) family present in many bacteria. The protein namedT. thermophilus CRP is highly homologous to the CRP family proteins from the phylaFirmicutes ,Actinobacteria , andCyanobacteria , and it forms a homodimer and interacts with cAMP. CRP mRNA and intracellular cAMP were detected in this strain, which did not drastically fluctuate during cultivation in a rich medium. The expression of several genes was altered upon disruption of theT. thermophilus CRP gene. We found six CRP-cAMP-dependent promoters in in vitro transcription assays involving DNA fragments containing the upstream regions of the genes exhibiting decreased expression in the CRP disruptant, indicating that the CRP is a transcriptional activator. The consensusT. thermophilus CRP-binding site predicted upon nucleotide sequence alignment is 5′-(C/T)NNG(G/T)(G/T)C(A/C)N(A/T)NNTCACAN(G/C)(G/C)-3′. This sequence is unique compared with the known consensus binding sequences of CRP family proteins. A putative −10 hexamer sequence resides at 18 to 19 bp downstream of the predictedT. thermophilus CRP-binding site. The CRP-regulated genes found in this study comprise clustered regularly interspaced short palindromic repeat (CRISPR)-associated (cas ) ones, and the genes of a putative transcriptional regulator, a protein containing the exonuclease III-like domain of DNA polymerase, a GCN5-related acetyltransferase homolog, andT. thermophilus -specific proteins of unknown function. These results suggest a role for cAMP signal transduction inT. thermophilus and imply theT. thermophilus CRP is a cAMP-responsive regulator.