On the 230-kilobase-pair (kb) virulence plasmid of Shigella flexneri 2a strain YSH6000, at least seven separate genetic determinants have been identified. One of them, an approximately 4-kb region, virG, that is required for the Sereny reaction, was extensively studied to examine the role of the virG region. The phenotype of a VirG-mutant (M94) of YSH6000 in the cytoplasm of cultured MK cels was characterized by a kinetic study of the invading shigellae. The observed phenotype of M94 in the cytoplasm indicated that the virG locus is not required for multiplication of the invading shigellae, but is essential for their spread to adjacent cells. The DNA region necessary for the VirG function was localized to a 3.6-kb DNA sequence on the 230-kb plasmid. A 130-kilodalton polypeptide was confirmed to be the virG product. External labeling of bacteria with 1251 indicated that the 130-kilodalton virG protein is exposed on the bacterial surface. The nucleotide sequence of 4,472 bp, which contains the functional virG gene and its own regulatory sequence, was determined, and a large open reading frame encoding 1,102 amino acid residues was identified.

The expression of plasmid-encoded, invasion-related antigens lpa b, c and d of Shigella flexneri was found to be positively regulated at transcriptional level by a 33kD protein produced by the previously defined, virulence-associated Region 1 on the SalI fragment B of the 230 kb invasion plasmid. The gene (designated virB) was identified and its nucleotide sequence determined. No Ipa b or c was produced in the absence of an intact virB gene although lower levels of d were produced. The previously reported regulatory activity of the virF gene some 30 kb distance away was shown to act exclusively through virB. In contrast, the activation of the virG gene necessary for intercellular spread occurred directly by virF without the requirement for virB. This study thus ascribes a critical function to a previously recognized, but functionally undefined, virulence locus on the large invasion plasmid of S. flexneri. The virF gene appears to have a central role in activation of the 230 kb plasmid-encoded virulence genes.

Active remodeling of the coronary artery lesions in Kawasaki disease continues in the form of luxuriant intimal proliferation and neoangiogenesis for several years after the onset of the disease. This process is distinct from adult-onset atherosclerosis.

The genetic determinants required for invasion of epithelial cells by Shigellaflexneri and for the subsequent bacterial spreading are encoded by the large virulence plasmid. Expression of the virulence genes is under the control of various genes on the large plasmid as well as on the chromosome. We previously identified one of the virulence-associated loci near phoBR in the NotI-C fragment of the chromosome of S. flexneri 2a YSH6000 and designated the locus vacC. The vacC mutant showed decreased levels of IpaB, IpaC, and IpaD proteins as well as transcription of ipa, an operon essential for bacterial invasion (N.