Abstract
The transport and phosphorylation of gluconate in E. coli occurs through two systems (GntI and GntII) which duplicate activities. __bio__H‐asddeletion mutants do not grow on media with gluconate as sole carbon source because they lack the GntI system and do not express GntII. Although E. coli C177 is a Δ(__bio__H‐asd) mutant, it carries the __pyr__B linked mutation __gnt__177 that enables it to metabolize this substrate through inducible expression of the GntII system. Several __gnt__S derivatives which are unable to grow on gluconate were isolated from E. coli C177 by spontaneous curing of the transposon Tn10 previously inserted at the __gnt__S locus (zjf::Tn10, min 95.3). A representative __gnt__S mutant, E. coli TI141A retained the ability to take up gluconate but had lost the thermosensitive gluconokinase activity (gene __gnt__V, min 96.9). Furthermore, it could be demonstrated that __gnt__V is repressed in E. coli TI141A. The results indicate that __gnt__S might specify a trans‐acting positive regulator involved in the control of at least the expression of the thermosensitive gluconokinase (GntII), instead of a gluconate uptake system as it was previously postulated. Likewise, these results can be used to reconsider whether the locus altered by the __gnt__177 lesion is allelic with that of the GntII permease instead of a regulator, as it was originally postulated.