The consumption of lignin by a Streptomyces bacterium is a multistep process, which requires the bacteria to release extracellular enzymes to break down lignin into smaller compounds. The smaller compounds can then be taken up by the bacteria as a carbon and energy source. In a recent paper published in Nucleic Acids Research, researchers discovered that one of the lignin-derived compounds that the Streptomyces bacteria can use is protocatechuate. A cluster of genes that encode enzymes for breaking down protocatechuate were only expressed in the presence of protocatechuate. The researchers discovered PcaV a DNA-binding protein involved in the regulation of the protocatechuate-degrading gene cluster. In a series of experiments they first established that PcaV tightly binds to specific DNA sequences in close proximity to the protocatechuate-degrading gene cluster. Second, they found that PcaV loses its affinity for DNA in the presence of the compound protocatechuate.

For the protocatechuate-degrading gene cluster in the Streptomyces, what type of gene regulation is being used? Please describe the role of protocatechuate and draw the operon structure of protocatechuate-degrading gene cluster.