Jc. Gutierrez et al., NASST, 2 GENES INVOLVED IN THE INDUCTION OF THE ASSIMILATORY NITRITE-NITRATE REDUCTASE OPERON (NASAB) OF AZOTOBACTER-VINELANDII, Molecular microbiology, 18(3), 1995, pp. 579-591
An operon including two new genes (nasS and nasT) has been defined, cl
oned and sequenced. The deduced NASS protein is homologous to NRTA fro
m Synechococcus sp. and to NASF from Klebsiella pneumoniae, two protei
ns involved in nitrate uptake. The predicted NAST polypeptide is homol
ogous to the regulator proteins of the two-component regulatory system
s. NASS plays a negative regulatory role in the synthesis of the nitra
te and nitrite reductase. NAST is required for the expression of the n
itrite-nitrate reductase operon (nasAB). Expression of the nasST opero
n is not under the control of the NTR system and is not regulated by t
he nitrogen source. A Phi(nasA-lacZ) fusion has been used to analyse e
xpression of the nasAB operon in three different genetic backgrounds w
ith altered nitrate reductase activity. Beta-galactosidase activity in
two of them was independent of nitrate but in a mutant unable to redu
ce nitrate, nas-4 it was normally induced by nitrate.