ISOLATION AND INITIAL CHARACTERIZATION OF THE URIDINE PHOSPHORYLASE FROM SALMONELLA-TYPHIMURIUM

The structural udp gene encoding uridine phosphorylase (UPase) was clo ned from the Salmonella typhimurium chromosome and overexpressed in E, coli cells. The S, typhimurium UPase was purified to an apparently ho mogeneous state, and some physicochemical characteristics of the enzym e were studied. The molecular weight of one subunit of UPase is 27.5 k D, and the optimal pH for its activity is 7.2-7.4. The native S, typhi murium UPase consists of six identical subunits, and its molecular wei ght is about 165 kD. According to these parameters, the S. typhimurium UPase is similar to the E. coli UPase. However, these enzymes differ substantially from one another by the substrate specificity and sensit ivity to polarity of the medium. The S, typhimurium UPase has much hig her phosphorylation activity toward thymidine, deoxyuridine,and 5'-bro mide- or 5'-fluoride-containing analogs of nucleosides than E. coli UP ase.