DEMONSTRATION OF A HEAT-STABLE 120-KILODALTON PROTEIN OF RICKETTSIA-JAPONICA AS A SPOTTED-FEVER GROUP-COMMON ANTIGEN

Genomic libraries of Rickettsia japonica were cloned into an expressio n vector lambda gtl11. A clone expressing a protein reactive with anti serum against 120-kilodalton (kDa) proteins, a mixture of heat-modifia ble and heat-stable polypeptides, was selected and designated as lambd a Rj120-1. The expressed protein has a molecular mass of 180 kDa. West ern immunoblotting demonstrated that the expressed protein was a fusio n protein with beta-galactosidase. The antiserum against 120-kDa prote ins was absorbed by the induced lysogen, resulting in the removal of r eactivity to the heat-stable 120-kDa polypeptide. The antiserum agains t the expressed protein reacted with heat-stable 120- to 130-kDa polyp eptides of spotted fever group (SFG) rickettsiae in addition to R.japo nica. The findings indicated that the protein expressed from the clone d gene of R. japonica possessed the antigenicity group-common to SFG r ickettsiae. Primers designed from the gene coding for R. conorii heat- stable 120-kDa protein (Schuenke, K.W., and Walker, D.H., Infect. Immu n. 62: 904-909, 1994) and Xgtll lacZ gene amplified the lambda Rj120-1 DNA by the polymerase chain reaction (PCR), Analysis of restriction f ragment length polymorphism (RFLP) of the PCR-amplified products revea led that the cloned DNA corresponds to a portion of the gene coding fo r the heat-stable 120-kDa protein of R. conorii with 2,519 nucleotides beginning at nucleotide 190 of the open reading frame, RFLP demonstra ted that the cloned gene was highly homologous to the corresponding ge ne of R. conorii.