CHARACTERIZATION OF A NOVEL PECTATE LYASE FROM ERWINIA-CAROTOVORA SUBSP CAROTOVORA

The pectate lyase (Pel, EC 4.2.2.2) isoenzyme profile of Erwinia carot ovora subsp. carotovora was characterized by isoelectric focusing, and the corresponding genes coding for four different exported Pels were cloned. The nucleotide sequence of the pelB gene encoding one of these isoenzymes was determined and was shown to contain 1,040-bp open read ing frame coding for a 37,482-Da protein with a putative cleavable ami no terminal signal peptide. Overexpression and selective labeling expe riments with the pelB clone demonstrated the synthesis of a 35-kDa pol ypeptide, which is in accordance with the deduced size of the processe d PelB. The predicted amino acid sequence of PelB was very similar to that of Pel-3 of another E. c. subsp. carotovora strain 71, but showed no similarity to other previously characterized pectinolytic enzymes. The pelB gene is located next to the previously characterized pehA ge ne encoding an endopolygalacturonase. The two genes are divergently tr anscribed from a common control region and are subject to similar glob al regulation by the central virulence regulator exp1. Inactivation of pelB did not appear to reduce the virulence of the mutant strain, sug gesting that pelB does not have a major role in pathogenicity. Unlike other Pels, PelB required partially methyl enterified pectin as substr ate suggesting that PelB represents a novel isoform of pectate lyase.