Fig. 3.

LuxR directly activates transcription of qrr2, qrr3 and qrr4 in E. coli. The constitutively active luxO allele, luxOD47E, was recombined onto the chromosome of E. coli strain MC4100 at the λ_att site. Flow cytometry was used to measure fluorescence production (in arbitrary units) from WT V. harveyi qrr promoter-gfp fusions and the qrr promoters with the LuxR-binding sites mutated (qrr^luxR-bs). The measurements were made in the presence and absence of LuxR. E. coli strains: KT1646 (qrr1-gfp), KT1648 (qrr1-gfp + luxR), KT1529 (qrr2-gfp), KT1530 (qrr2-gfp + luxR), KT1535 (qrr2^luxR-bs-gfp), KT1536 (qrr2^luxR-bs-gfp + luxR), KT1531 (qrr3-gfp), KT1532 (qrr3-gfp + luxR), KT1614 (qrr3^luxR-bs-gfp), KT1615 (qrr3^luxR-bs-gfp + luxR), KT1533 (qrr4-gfp), KT1534 (qrr4-gfp + luxR), KT1539 (qrr4^luxR-bs-gfp), KT1540 (qrr4^luxR-bs-gfp + luxR), KT1647 (qrr5-gfp), KT1649 (qrr5-gfp + luxR). Background fluorescence was measured in the absence of LuxO˜P which averaged around 20 units (data not shown). Cultures were grown in triplicate and error bars denote standard deviation of the mean.