B. Demers et al., INDUCTION OF TYPE-III SECRETION IN SHIGELLA-FLEXNERI IS ASSOCIATED WITH DIFFERENTIAL CONTROL OF TRANSCRIPTION OF GENES ENCODING SECRETED PROTEINS, EMBO journal, 17(10), 1998, pp. 2894-2903
Shigella, the etiological agent of human bacillary dysentery, invades
the colonic epithelium where it induces an intense inflammatory respon
se. Entry of Shigella into epithelial cells involves a type III secret
ion machinery, encoded by the mxi and spa operons, and the IpaA-D secr
eted proteins. In this study, we have identified secreted proteins of
46 and 60 kDa as the products of virA and ipaH9.8, respectively, the l
atter being a member of the ipaH multigene family. Inactivation of vir
A did not affect entry into epithelial cells. Using lacZ transcription
al fusions, we found that transcription of virA and four ipaH genes, b
ut not that of the ipaBCDA and mxi operons, was markedly increased dur
ing growth in the presence of Congo red and in an ipaD mutant, two con
ditions in which secretion through the Mxi-Spa machinery is enhanced.
Transcription of the virA and ipaH genes was also transiently activate
d upon entry into epithelial cells. These results suggest that transcr
iption of the virA and ipaH genes is regulated by the type III secreti
on machinery and that a regulatory cascade differentially controls tra
nscription of genes encoding secreted proteins, some of which, like vi
rA, are not required for entry.