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
.