FIGURE 2.

Wild-type and mutant constructs assayed for DIVa binding by plating and FACS assays for GFP expression. E. coli DH5α containing pBDG-LtrA or mutants diagrammed schematically to the left were induced with L-arabinose (+Ara), and GFP fluorescence was monitored by plating and FACS assays, as described in the Materials and Methods. The plating assays for the different constructs were done in parallel. The FACS profiles show the numbers of cells in a window of fluorescence intensity before (purple) and after (green) L-arabinose induction. The constructs tested were: (A) pBDG-LtrA; (B) pBDG, identical to pBDG-LtrA but lacking the LtrA ORF; (C,D) pBDG-LtrA(M1-DIVa) and pBDG-LtrA(M2-DIVa), mutants in which the sequence 5′-AAAACCTCAA between the SD sequence and initiation codon in DIVa was replaced by 5′-AgAtataCAt and 5′-ttAAaaTaAA, respectively (see Fig. 1; lowercase letters indicate mutant nucleotide residues). (E) pBDG-LtrA/ΔN10, which expresses a mutant LtrA protein with an N-terminal truncation of 10 amino acid residues. Mutated regions are shown in red.