FIG. 3.

The LeuO protein plays a trans-acting role in leu-500 activation. (A) The relevant regions in the linear maps of pWU804T, pWU804TR, and pWU802T in which pleuO was replaced by ptac are shown. The orientations of the promoters are indicated (arrows). pSO1000 was used in this experiment to provide lac repressor (24). Primer extension results for transcripts initiated from pleu-500 with RNAs isolated from CH582 are shown (lanes 1 to 5). The testing conditions are indicated above the lanes. (B) Part of the peptide sequence of the 942-bp leuO gene coding region product is illustrated in the linear map of pWU804H. The helix-turn-helix motif located at positions 39 to 58 of the LeuO peptide (12) (boxed) and the R41P mutation within this motif are indicated. The map of expression vector pEV101, which is used to supply wild-type LeuO in trans upon IPTG induction, is also shown. Primer extension results obtained with pWU804 and pWU804H in the absence of pEV101 are shown for transcripts initiated from pleuO (lanes 1 and 3, respectively) and transcripts from pleu-500 (lanes 2 and 4, respectively). In the presence of pEV101, pleu-500 activity was detected by using RNAs isolated from pWU804H-harboring CH582 without or with IPTG treatment (lanes 5 and 6, respectively).