1b), confirming that the NMA0797/0798 TCS was involved in the induction of the expression of the pilC1 gene during N. meningitidis–host cell interaction (Jamet et al., 2009). Moreover,

in mutant KZ1CNMA1803, the β-galactosidase activity was induced upon contact with host cells at a level significantly higher than that in the wild-type KZ1C strain (P<0.01) (Fig. 1b). To confirm these data, the NMA1803 mutation was introduced into the parental N. meningitidis strain 8013 that is devoid of pilC1-lacZ fusion. Total RNA was isolated from the wild-type 8013 and the 8013NMA1803 mutant strain grown in an infection medium and harvested after 1 and 4 h of adhesion to HUVECs. The level of transcription of pilC1 was measured using real-time quantitative RT-PCR. The results confirmed the

Y27632 increased level of pilC1 induction in mutant 8013NMA1803 compared with that RGFP966 nmr of the wild-type 8013 strain (data not shown). Altogether, these data demonstrated that insertion of a transposon into gene NMA1803 resulted in augmented expression of the pilC1 gene upon contact with host cells. Analysis of the genomic location of the NMA1803 gene revealed that it is located in a putative operon spanning from gene NMA1802 to gene NMA1806 (Fig. 2a). Because gene NMA1802 belongs to the REP2 regulon, which is upregulated upon contact with host cells (Morelle et al., 2003), we first investigated whether the expressions of the genes located downstream 17-DMAG (Alvespimycin) HCl of gene NMA1802, i.e. genes NMA1803, NMA1805 and NMA1806, were also regulated upon interaction with host cells. The level of transcription of genes NMA1802–NMA1806 was determined using quantitative RT-PCR from total RNA isolated from strain 8013 grown in an infection medium and from bacteria adherent

to HEC-1B cells. This revealed that the expression of the four genes was coordinately induced upon contact with host cells (Fig. 2b). Moreover, NMA1803 and NMA1805 are overlapping ORFs (Fig. 2a; Vallenet et al., 2006). Analysis of the cotranscription of adjacent genes by RT-PCR revealed that the adjacent NMA1802–NMA1803 and NMA1805–NMA1806 genes were cotranscribed (Fig. 2c). Altogether, these data demonstrated the operonic organization of genes NMA1802–NMA1806. As a corollary, the REP2 sequence that is located upstream of gene NMA1802 contains a promoter for the whole operon, thus being consistent with the above data showing an upregulation of genes NMA1802–NMA1806 following adhesion onto host cells. According to database annotations, NMA1803 is a pseudogene that is part of a putative two-component system, where NMA1803 is encoding the putative sensor and NMA1805 the putative regulator (Vallenet et al., 2006). The protein encoded by NMA1803 lacks the cytoplasmic transmitter and nucleotide-binding domains found in functional sensors (Snyder et al.