| Abstract: | Cosmid clone banks of Rickettsia prowazekii genomic DNA were established in Escherichia coli and screened for expression of the rickettsial carrier-mediated ADP/ATP translocator. Out of 2700 clones screened, a single clone, designated MOB286, accumulated radioactivity when incubated with [alpha-32P]ATP in 100 mM sodium phosphate buffer. This clone carried a plasmid, pMW286, containing a 9-kilobase-pair insert of rickettsial DNA, as established by DNA X DNA hybridizations. Transformation studies with purified pMW286 established that the ability of E. coli cells to accumulate radioactivity was mediated by the recombinant plasmid. Results from experiments in which [3H]ATP was substituted for [alpha-32P]ATP strongly suggested that the radiolabeled ATP was transported intact. Furthermore, [3H]ATP was incorporated into 10% (wt/vol) trichloroacetic acid-precipitable material in a time-dependent manner. Uptake of ATP was also temperature-dependent, insensitive to atractyloside, N-ethylmaleimide, and dinitrophenol, and specific for ADP and ATP. Efflux of radiolabeled nucleotide was observed in the presence of extracellular ADP or ATP but not AMP and was not observed in the absence of extracellular adenine nucleotides. The successful cloning and expression of the rickettsial ADP/ATP translocator in E. coli will permit better characterization of rickettsial bioenergetics and of the metabolic regulation of obligate intracellular parasitism. |
