Expression in Spiroplasma citri of an epitope carried on the G fragment of the cytadhesin P1 gene from Mycoplasma pneumoniae

We have previously described the use of the replicative form (RF) of Spiroplasma citri virus SpV1 as a vector for cloning and expressing foreign genes in S. citri, an organism which reads UGA as a tryptophan codon (C. Stamburski, J. Renaudin, and J.M. Bové, J. Bacteriol. 173:2225-2230, 1991). We now report cloning and expression in S. citri of the G fragment of cytadhesin P1 gene from Mycoplasma pneumoniae. The G fragment was inserted in the SpV1 RF downstream of a synthetic ribosome binding site and introduced into S. citri by electroporation. Northern (RNA) blot analyses showed that in S. citri, the G fragment was transcribed from an SpV1 RF promoter as a 1.2-kb mRNA. The translation product was detected by Western blotting (immunoblotting) with a rabbit antiserum raised against total proteins from M. pneumoniae (strain FH) and was proved to be P1 specific by using monoclonal antibodies specific for the G region of the P1 protein. The apparent molecular mass of the polypeptide (24.5 kDa) indicates that in S. citri, the G fragment was fully translated in spite of the seven UGA codons present in the reading frame.