Characterization of a Novel Pectate Lyase from Erwinia carotovora subsp. carotovora. Riikka Heikinheimo. Department of Molecular Genetics, Uppsala Genetic Center, Swedish University of Agricultural Sciences, Box 7010, S-75007 Uppsala, Sweden. Diana Flego, Minna Pirhonen, Maj-Britt Karlsson, Anders Eriksson, Andres Mae, Viia Koiv, and E.Tapio Palva Department of Molecular Genetics, Uppsala Genetic Center, Swedish University of Agricultural Sciences, Box 7010, S-75007 Uppsala, Sweden. MPMI 8:207-217. Accepted 14 November 1994. Copyright 1995 The American Phytopathological Society.

The pectate lyase (Pel, EC 4.2.2.2) isoenzyme profile of Erwinia carotovora subsp. carotovora was characterized by isoelectric focusing, and the corresponding genes coding for four different exported Pels were cloned. The nu-cleotide sequence of the pelB gene encoding one of these isoenzymes was determined and was shown to contain 1,040-bp open reading frame coding for a 37,482-Da protein with a putative cleavable amino terminal signal pep-tide. Overexpression and selective labeling experiments with the pelB clone demonstrated the synthesis of a 35-kDa polypeptide, which is in accordance with the deduced size of the processed 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 gene encoding an endopolygalacturonase. The two genes are divergently transcribed from a common control region and are subject to similar global regulation by the central virulence regulator expl. Inactivation of pelB did not appear to reduce the virulence of the mutant strain, suggesting that pelB does not have a major role in pathogenicity. Unlike other Pels, PelB required partially methyl esterified pectin as substrate suggesting that PelB represents a novel isoform of pectate lyase.