The L-Ara4N-mediated negative feedback is not limited to PmrA-dependent genes specifying LPS-modifying enzymes , because mRNA levels of the PmrA-activated aroQ ( Tamayo et al. , 2005b ) , which encodes a chorismate mutase , are lower in the wild-type than in the ugd mutant at 120 min , even though these strains produce similar amounts of aroQ transcript at 20 min ( Figure S4A ) .