ABSTRACTIn bacteria, polynucleotide phosphorylase (PNPase) is one of the main exonucleolytic activities involved in RNA turnover and is widely conserved. In spite of this, PNPase does not seem to be essential for growth if the organisms are not subjected to special conditions, such as low temperature. We identified the PNPase-encoding gene (pnp) ofPseudomonas putidaand constructed deletion mutants that did not exhibit cold sensitivity. In addition, we found that the transcription pattern ofpnpupon cold shock inP. putidawas markedly different from that inEscherichia coli. It thus appears thatpnpexpression control and the physiological roles in the cold may be different in different bacterial species.