As the key obligatory step in the glycolytic pathway, the regulation of phosphofructokinase (PFK-1) has been the focus of study of several laboratories. While standard cloning procedures have opened the door to study PFK from a vast array of sources, a good pfk knockout Escherichia coli strain has not previously been developed. Many laboratories rely on DF1020 or similar derivatives for PFK expression. Unfortunately, DF1020 grows poorly and does not have an inherent means for controlling expression of genes from plasmids. More importantly, however, DF1020 has a tendency to grow on minimal media when glucose is used as the sole carbon source. In this study, a new E coli PFK expression strain lacking both PFK-1 and PFK-2 has been engineered using lambda-red mediated chromosomal deletion. The resulting strain has been designated RL257. In addition to having both pfkA and pfkB deleted, RL257 contains the lacI(q) allele, which allows for inducible expression when coupled with an expression vector! containing either the lac or tac promoter. (c) 2005 Elsevier Inc. All rights reserved.