CHARACTERIZATION OF THE AMSI GENE-PRODUCT AS A LOW-MOLECULAR-WEIGHT ACID-PHOSPHATASE CONTROLLING EXOPOLYSACCHARIDE SYNTHESIS OF ERWINIA-AMYLOVORA

The ams region, responsible for amylovoran synthesis of the fireblight pathogen Erwinia amylovora, contains the gene amsI encoding a 144 ami no acid protein with homology to mammalian low molecular weight acid p hosphatases [Bugert and Geider (1995) Mol. Microbiol. 15, 917-933]. A DNA fragment with amsI was cloned under the control of the lac promote r on a high copy number plasmid. The gene product of amsI is about 17 kDa in a protein expression system and had the enzymatic activity of a n acid phosphatase. This is the first report about a low molecular wei ght acid phosphatase activity in prokaryotes. As part of the large ams transcript, expression of amsI was affected by the activator proteins RcsA and RcsB. Over-expression of amsI in E. amylovora caused a stron g increase of acid phosphatase activity, but additionally a strong red uction in EPS synthesis, phenotypically similar to a mutation in the g ene. The gene product may participate in changes of phosphorylation re quired for the biosynthesis of EPS such as recycling the Lipid carrier diphosphate to the monophosphate form.