Dm. Anderson et O. Schneewind, Yersinia enterocolitica type III secretion: an mRNA signal that couples translation and secretion of YopQ, MOL MICROB, 31(4), 1999, pp. 1139-1148
Pathogenic Yersinia species export Yop proteins via a type III machinery to
escape their phagocytic killing during animal infections. Here, we reveal
the type III export mechanism of YopQ. In the presence of calcium, when typ
e III secretion was blocked, yopQ mRNA was not translated. The signal of Yo
pQ sufficient for the secretion of translationally fused reporter proteins
was contained within the first 10 codons of its open reading frame. Some fr
ameshift mutations that completely altered the peptide sequence specified b
y this signal did not impair secretion of the reporter protein. Exchanging
the upstream untranslated mRNA leader of yopQ for that of E. coli lacZ also
did not affect secretion. However, removal of the first 15 codons abolishe
d YopQ export. Pulse-labelled YopE, but not YopQ, could be secreted after t
he polypeptide had been synthesized within the cytoplasm of Yersinia (post-
translational secretion). Thus, YopQ appears to be exported by a mechanism
that couples yopQ mRNA translation with the type III secretion of the encod
ed polypeptide.