A-029. Inactivation of nikD Affects the Activity and Expression of MarA in Escherichia coli

C. Ruiz Rueda, S. B. Levy;
Tufts Univ. Sch. of Med., Boston, MA.

MarA is transcriptional regulator of Escherichia coli specified by the marRAB operon. MarA directly activates or represses multiple chromosomal genes, affecting many functions including multiple antibiotic resistance (Mar), virulence, and survival. To find genes that affect the function of MarA, we carried out random transposome mutagenesis of cells in which a hdeABp-lacZ chromosomal transcriptional fusion was repressed by MarA (white colonies), selecting mutant colonies that were blue (hdeAB not repressed). We identified several genes whose inactivation prevented repression of hdeAB by MarA, and we focused on nikD. This gene belongs to the nikABCDER operon, which is involved in nickel uptake, and encodes a nickel permease ATPase subunit. nikD is not known to be in the Mar regulon. Interestingly, inactivation of nikD prevented also autoactivation of the marRAB operon by MarA, indicating that this mutation affects the activity of MarA on both activated and repressed genes. Functional complementation of the nikD inactivation by the addition of 0.5 mM nickel did not restore the activity of MarA, which suggests that the loss of activity of MarA is not related to a lack of nickel uptake. Further research is in progress to understand the relationship between MarA and the nikABCDE nickel transporter. The findings from this approach show the involvement of other chromosomal genes in MarA activity.