[3] Isolation of mutants in the l-arabinose gene-enzyme complex

"In vivo" detection of L-arabinose-binding protein, CRM-negative mutants

An "in vivo" assay for the detection of mutants negative to CRM (cross-reacting material) is described. l-Arabinose-negative mutants of Escherichia coli B/r were grown on Casamino Acids-l-arabinose plates to which a 3-ml agar layer, containing antiserum to the l-arabinose-binding protein (ABP), had been applied. After incubation and partial lysis of the clones "in situ," the plates were refrigerated for 36 hr, rinsed of colonial growth with water, and observed for the presence or absence of an immune precipitation. ABP-minus and l-arabinose regulator (araC)-minus mutants do not produce a precipitin reaction. l-Arabinose isomeraseless (EC 5.3.1.4; araA), kinaseless (EC 2.7.1.16; araB), and epimeraseless (EC 5.1.3.a; araD) mutants produce precipitin reactions. Mutants of E. coli B/r generated by treatment of the wild type with ethyl methane sulfonate or ultraviolet irradiation were isolated, tested for l-arabinose uptake, and screened for the presence or absence of ABP by the described assay. The applications of such an assay are discussed.

L-arabinose binding protein from Escherichia coli B-r

A protein which is capable of binding l-arabinose-1-(14)C has been isolated from l-arabinose-induced cultures of Escherichia coli B/r. Analysis for this l-arabinose-binding protein (ABP) in a number of l-arabinose-negative mutants suggests that the ABP is not coded for by any of the known genetic units of the l-arabinose complex yet is under the control of the regulator gene araC. The ABP has been purified and found to bind l-arabinose, d-fucose, d-xylose, and l-ribulose with decreasing affinities. The K(m) for l-arabinose is 5.7 x 10(-6)m. The molecular weight, as determined by equilibrium centrifugation, was found to be 32,000. The protein was observed to have many features that liken it to other recently isolated binding proteins that have been implicated in the active transport of small molecules.