MTRR and infection: The mtrCDE locus is under the control of two classical DNA binding proteins: the Mtr repressor (MtrR) protein, which down regulates expression of the mtrC transcript and presumably other proteins in the operon [27], and the Mtr activator (MtrA) [28], which enhances expression of mtrCDE. Several studies have shown that mutations of MtrR lead to enhanced fitness of N. gonorrhoeae in a mouse model of infection, suggesting that this system may also be crucial for survival of the organism in the human host [38,39].