FIGURE 4.

S1 and PNPase expression following S1 depletion (panels A and B) or overexpression (panel C). The panels show Western blotting with S1 (A and upper part of C) or PNPase (B and lower part of C) specific antibodies of 10% SDS-polyacrylamide gels transferred onto nitrocellulose sheets and revealed with ECL Western blotting reagent. (A) Cultures of C-5698 (pnp⁺) or C-5707 (Δpnp-751) were grown in LD with arabinose and diluted 1:4 in LD with glucose as described in the Materials and Methods. Samples were taken for protein extraction before (t = 0) and at different time after dilution (indicated in hours on top of the lanes). One microgram of crude extract was loaded on each lane. (B) Cultures of C-5698 were grown in LD with arabinose up to OD₆₀₀ = 0.2; the cells were then washed with LD, collected in a small volume of broth, resuspended in 1 vol of LD supplemented with arabinose or glucose or diluted twofold or fourfold (dilution factor [DF] of 1, 2, and 4, respectively) in the same media. Incubation at 37°C was continued and samples were taken at the OD₆₀₀ reported in the figure. Crude extracts obtained from 0.1 OD₆₀₀ units of cell cultures were loaded on each lane. (C) Cultures at OD₆₀₀ = 0.4 of C-1a (pnp⁺) or C-5691 (Δpnp-751) carrying pREP4 and pQE31-S1 plasmids were split in two and one subculture was induced with 1 mM IPTG. Samples for protein extraction were taken immediately before and at the time indicated in minutes on top of the lanes after addition of IPTG. One (pnp⁺) or 0.5 (Δpnp-751) μg of crude extracts were loaded on each lane.