The fliU and fliV genes are expressed as a single ORF in Salmonella choleraesuis

A DNA fragment carrying flagellar genes was cloned from Salmonella cholerae suis. Compared to the corresponding DNA fragment of Salmonella muenchen, th is fragment contained three ORFs instead of four shown in S. muenchen. The DNA sequence data showed that there was an insertion of nucleotide C in the ORF of the S. choleraesuis fliU gene, which resulted in the disappearance of a termination codon downstream. The recombinant plasmid pFU11 containing the coding region of the fliU gene made by PCR on S. choleraesuis genomic DNA was constructed and expressed in Escherichia coli in the presence of IP TG. As expected, a 45 kDa protein band was observed on a SDS-PAGE gel, in c ontrast to two with each having about a half of the molecular weight. These results demonstrated that the DNA sequence encoding one protein (FliU) in S. choleraesuis corresponded to the DNA sequence encoding two proteins (Fli U and FliV) in S. muenchen. The protein encoded by this single ORF might ca rry out the functions of two separated proteins by folding in such a way th at its conformation could function like two interdependent protein subunits .