Specific binding of the first enzyme for histidine biosynthesis to the DNA of the histidine operon

Studies were done to examine direct binding of the first enzyme ofthe histidine biosynthetic pathway (phosphoribosyltransferase) to 32Plabeied ø80dhis DNA and competition of this binding by unlabeled homologous DNA and by various preparations of unlabeled heterologous DNA, including that from a defective ø80 bacteriophage carrying the histidine operon with a deletion of part of its operator region. Our findings show that phosphoribosyl transferase binds specifically to a site in or near the regulatory region of the histidine operon. The stability of the complex formed by interaction of the enzyme with the DNA was markedly decreased by the substrates of the enzyme and was slightly increased by the allosteric inhibitor, histidine. These findings are consistent with previous data that indicate that phosphoribosyl transferase plays a rolein regulating expression of the histidine operon.