Results 
Role of FimR in mfa1 expression The fimA gene is the only gene known to be tightly controlled by the FimS/FimR system.
It was postulated that the expression of other genes may also be controlled by this two component regulatory system.
To investigate effects of FimR on expression of the mfa1 gene, an insertional fimR mutant was constructed by allelic replacement.
Expression of fimA and mfa1 in the fimR- mutant was determined using real-time PCR analysis.
Statistically significant differences of the level of gene expression in 33277 and the fimR- mutant were calculated by a Student's t-test.
As shown in Fig. 1a, expression of the fimA gene was abolished in the fimR- mutant strain FRE.
This result is consistent with previous observations (Hayashi et al., 2000; Nishikawa et al., 2004).
The striking finding is that expression of the mfa1 gene was also repressed threefold in the fimR- mutant, although not to the degree observed with the fimA expression.
However, the fimR- mutation had no effect on expression of rgpA, a gene encoding the arginine-specific protease, or the P. gingivalis 16S RNA gene.
This analysis suggests the FimS/FimR system is required for expression of both major and minor fimbriae.
To determine production of long (major) and short (minor) fimbriae in the fimR- mutant, western blotting was performed with a polyclonal anti-FimA or anti-Mfa1 antibody to compare fimbrial production in wild-type strain (33277), the fimR- mutant (FRE), the fimA- mutant (FAT) and the mfa1- mutant (MFAE).
Density of protein bands was determined by UVP Bioimaging System (UVP, CA).
This analysis revealed that the expression of the fimA and mfa1 genes was consistent at the mRNA level and protein level (Fig. 1b).
FimA protein was not detectable in the fimR- mutant, while a 50% lower level of Mfa1 protein was found in the fimR- mutant compared with that in wild-type strain 33277.
Similarly, there was no apparent change in RgpA production in the fimR- mutant, which was detected by anti-RgpA serum.
