| SarA |
+ |
An activator of the agrABCD operon activating P2
transcription. SarA is also
involved in agr-independent pathways via binding to conserved regions,
termed Sar boxes, within the promoters of several cell-wall-associated
proteins and exoproteins. |
(44, 45, 87, 88) |
| SarR |
– |
SarR represses P2 transcription
and binding of SarR to the sarA promoter represses
SarA expression. |
(18, 45) |
| SarS |
– |
Activates protein A (spa) and represses α-toxin
(hla) transcription |
(18, 89) |
| SarT |
– |
Activation of sarT results
in up-regulation of sarS, thus leading
to hla repression and spa activation. |
(18, 44) |
| SarU |
+ |
sarU is
repressed by SarT which in turn is down-modulated by agr. Since sarU is an activator of agr expression, this will lead to amplification of the original agr signal. |
(18, 44) |
| Rot |
– |
Represses toxin synthesis
and up-regulates cell wall protein synthesis. Rot affects the transcription
of 168 genes, many of which reflect an agr minus
phenotype. |
(90) |
| SarX |
– |
SarX acts as a negative
regulator of agr. Furthermore, MgrA is an activator
of sarX, thus implying an additional regulatory loop
whereby mgrA can modulate agr expression. |
(91) |
| MgrA |
+ |
Regulates cell-wall
turnover
and activates the production of secreted toxins, proteases and is
a regulator of autolysis. The effect of MgrA on autolysis may be mediated
by SarV which is a positive regulator of several autolytic enzymes. |
(92−94) |
| SarZ |
+ |
A positive regulator of hla expression. A sarZ mutant of RN4220
had attenuated virulence in both silk worm and mouse infection models. |
(18, 95) |
| SarV |
– |
A regulator of autolysis
that is repressed by SarA and MgrA. A sarV mutant
was found to be more resistant to detergent- or cell wall antibiotic-mediated
lysis. |
(18, 96) |
