CHITINASE-B FROM SERRATIA-MARCESCENS-BJL200 IS EXPORTED TO THE PERIPLASM WITHOUT PROCESSING

A gene encoding a chitinase from Serratia marcescens BJL200 was cloned and expressed in Escherichia coli and S. marcescens. Nucleotide seque ncing revealed an open reading frame encoding a 55.5 kDa protein of 49 9 amino acids without a typical signal peptide for export. The cellula r localization of the chitinase was studied, using two types of cell f ractionation methods and immunocytochemical techniques. These analyses showed that the chitinase is located in the cytoplasm in E. coli, whe reas it is exported to the periplasm in 5. marcescens. Analysis of chi tinase isolated from periplasmic fractions of 5. marcescens carrying t he cloned gene showed that export of the enzyme is not accompanied by processing at the N-terminus. The chitinase did not show any of the ch aracteristics that have been proposed to direct the export of other no n-processed extracellular proteins such as the E. coli haemolysin and might therefore be secreted via a hitherto unknown mechanism.