b-Galactosidase assays. b-Galactosidase activity was measured at
30 uC as previously described (Trotochaud & Wassarman, 2004), and
activity is expressed in Miller units (DOD420 min21 per OD600 unit)
(Miller, 1972). Briefly, cultures inoculated from a single colony were
grown for 18 h in RDM, diluted approximately 1 : 100 in fresh
medium (to OD600 0.04) and grown for 24 h, at which time they were
analysed (24 h time point) or rediluted into fresh medium (1 : 100)
and grown for an additional 6 h prior to analysis (6 h time point).
Cell growth was at 37 uC for all strain backgrounds except those
containing the hisG–lacZ reporter, which was at 30 uC as it is a
‘system I’ lysogen that is temperature-sensitive (Rao et al., 1994). For
b-galactosidase assays, cells were lysed with SDS and chloroform. At
least three independent cultures per strain were used per experiment,
and experiments were repeated at least three times.