Cloning and characterization of a xylanase gene from corn strains of Erwinia chrysanthemi

The gene encoding a 42-kDa endoxylanase was cloned from Erwinia chrysanthemi strain D1. Sequencing of this gene, called xynA, showed that it encoded a primary protein product of 413 amino acids with an unusual and long (31 amino acid) leader peptide that was cleaved during secretion to the bacterial periplasm. This protein is distinct from xylanases in glycohydrolase families 10 and 11 and, instead, appears to be intermediate between families 5 and 30. The xynA gene is located downstream from a gene with high homology to ATP-dependent RNA helicases and the Escherichia coli recD gene. Large amounts of the mature xylanase were produced by E. coli cells carrying a T7 expression plasmid construct and the protein was isolated from the bacterial periplasmic fraction by chromatography on a CM Bio-gel column. Marker exchange mutagenesis of the xynA gene eliminated the ability of strain D1 to produce detectable extracellular xylanase activity but did not affect virulence on corn leaves.