Both the pmrF operon and pmrE are necessary for the PmrA-PmrB-regulated attachment of aminoarabinose to lipid-A ( 15 , 45 ) .
The absence of transcriptional linkage between the RpoN and the PmrA regulons was corroborated because no significant differences were observed when the expression of PmrAcontrolled genes ( pmrI , pmrC , pmrF , and ugd ) was compared either in a RpoN or in a 1 DrpoN strain grown in LB ( exponential or stationary-phase ) or in a low-Mg N-21 minimal-medium , which are PhoP-and PmrA-inducing conditions ( Soncini & Groisman , 1996 ) ( Fig. 3a and data not shown ) .
( a ) b-Galactosidase activities were determined for pmrI : : MudJ , pmrC : : MudJ , pmrF : : MudJ and ugd : : MudJ ( all PmrA-regulated genes ) in an rpoN ( W-1 t ) or in a DrpoN strain .