REGULATION OF PURINE BIOSYNTHETIC GENES EXPRESSION IN SALMONELLA-TYPHIMURIUM .4. O-C MUTATION SITE OF PURG AND ITS FUNCTION-ANALYSIS

Salmonella typhimurium 5' phosphoribosylformylglycinamide (FGAR) amido transferase encoded by purG gene catalyzes the conversion of FGAR to f ormylglycinamide ribonucleotide (FGAM) in the presence of glutamine an d ATP for the de novo purine nucleotide biosynthesis. purG gene is neg atively regulated by a repressor-operator system. The O+ purG and O-c purG were cloned respectively in vivo. Restriction enzymes analysis of preliminary clones pLBG-1 (O+) and pLBG-2 (O-c) were carried our. The hybrid plasmids pLB1933 (O+) and pLB1927 (O-c) containing 5' control region of purG were constructed and the DNA sequences were determined respectively. DNA sequences data showed that O-c mutation of purG occu rred at the 3rd position of 16 bp PUR box in the 5' control region (G --> A). Gel retardation experiment indicated that the repressor bound well with O+ PUR hox, bur nor with O-c PUR box. The result strongly su pported the idea that PUR box is the binding region of repressor prote in and the 3rd position base G of PUR box is essential for the binding function with repressor protein.