LONR9 CARRYING A SINGLE GLU(614) TO LYS MUTATION INHIBITS THE ATP-DEPENDENT PROTEASE LA (LON) BY FORMING MIXED OLIGOMERIC COMPLEXES

An unusual lon mutation (called lonR9) is dominant over the wild-type gene, which encodes the ATP-dependent protease La (Lon) in Escherichia coli, when present in multicopy plasmids. Here, we cloned and sequenc ed lonR9, and showed that the mutant gene carries a single point mutat ion in its open reading frame, which leads to replacement of Glu(614) by LYS The LonR9 protein and its poly-His-tagged form were purified to apparent homogeneity. Both of the purified proteins were capable of i nhibiting the ATP-dependent proteolysis and the protein-activated ATP hydrolysis by protease La. Furthermore, the His-tagged LonR9 protein w as found to form mixed oligomeric complexes with protease La, upon ana lysis by chromatography on a metal-chelating column. These results sug gest that the phenotypic dominance of the lonR9 mutant is due to the f ormation of mixed oligomeric complexes between LonR9 and protease La, in which the defective components prevent the function of the wild-typ e subunits. (C) 1998 Academic Press.