Reporter assay for positioning of proteins at the bacterial pole. (a) Maltose utilization phenotype of indicated E. coli MG1655 strains. icsA53-757, polar cytoplasmic derivative of IcsA; icsAΔ507-729, delocalized derivative of IcsA; p-icsA, full-length icsA. + or −, growth or absence of growth, respectively, on maltose minimal medium. Red colony, maltose utilization; white colony, maltose nonutilization on maltose MacConkey indicator agar. (b) Positions of IcsA53-757-CRP-GFP and IcsAΔ507-729-CRP-GFP in MG1655 crp. Arrows, polar foci of IcsA53-757-CRP-GFP. (c) Maltose utilization phenotype of MG1655 crp or crp cheA, carrying a plasmid carrying cheY::crp or cheZ::crp. Predicted CRP position, putative positioning of fusion based on observed maltose utilization phenotype. (d) Colony phenotype on indicator medium containing various sugars. Note the correlation of the specificity of the phenotype with multiple CRP-dependent operons being required for sugar utilization. N/A, not applicable. Bars, 5 mm.