Regulation of purine biosynthetic genes expression in Salmonella typhimurium IV O~c mutation site of purG and its function analysis

摘要

Salmonella typhimurium 5 phosphoribosylformylglycinamide (FGAR) ami dotransf erase encoded by purG gene catalyzes the conversion of FGAR to formylglycinarnide ribonucleotide (FGAM) in the presence of glutarnine and ATP for the de novo purine nucleotide biosynthesis purG gene is negatively regulated by a represser-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 out. 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 occurred at the 3rd position of 16 bp PUR box in the 5' control region (G-->A). Gel retardation experiment indicated that the represser bound well with O~+ PUR box, but not with O~c PUR box. The result strongly supported the idea that PUR box is the binding region of repressor protein and the 3rd position base Gof PUR box is essential for the binding function with repressor protein.