Permits nitrate and nitrate transport into E.coli. Involved in excretion of nitrite produced by the dissimilatory reduction of nitrate. Increased nitrate reductase activity is seen under hypoxic conditions, however this seems to be due to induction of the probable nitrate/nitrite transporter narK2 rather than increased enzyme activity of the probable nitrate reductase NarGHJI. A member of the dormancy regulon. Induced in response to reduced oxygen tension (hypoxia), low levels of nitric oxide (NO) and carbon monoxide (CO). It is hoped that this regulon will give insight into the latent, or dormant phase of infection. Induction by hypoxia is independent of nitrate and nitrate levels. Wild-type levels of nitrite production in aerobic cultures, but hypoxic cultures show no increase in nitrite production. This protein serves as an immunogenic antigen, inducing gamma-interferon responses in whole-blood cultures from M.tuberculosis-exposed adults in Uganda, The Gambia and South Africa, indicating this might be a good vaccine candidate. One of the activities induced in M.tuberculosis by hypoxia is the dissimilatory reduction of nitrate to nitrite, which serves to provide energy as the bacteria adapt to anaerobiosis. Belongs to the major facilitator superfamily. Nitrate/nitrite porter (TC 2.A.1.8) family.