FIG. 3.

The polymerization activity of PNPase is not essential for its cold shock function. E. coli wild-type, Δpnp, ΔpcnB, and Δpnp ΔpcnB cells were transformed with the pINIII plasmid alone as a control. The Δpnp and ΔpnpΔpcnB cells were also transformed with the pINIII plasmid containing PNPase, RNase II, or RNase R. The cells were streaked on LB plates containing ampicillin (50 μg ml⁻¹) and incubated at 15°C. Results for plates incubated for 96 h are presented.