Structure and organization of the pel genes from Erwinia chrysanthemi EC16.

The pelA and pelC genes from Erwinia chrysanthemi EC16 were sequenced and overexpressed in Escherichia coli cells. These genes and two others from the same strain that were characterized previously encode catalytically related pectate lyase proteins that are involved with the maceration and soft-rotting of plant tissue. The pel genes of strain EC16 were organized as two loosely linked clusters, with two structurally homologous genes in each. The pelA/E cluster also contained the remains of an additional pel gene, the 5' portion of which had been removed by a prior deletion event. Each of the four functional pel genes but not the deleted one contained an efficient rho-independent transcriptional terminator after the translational stop. These and other data indicate that the pel genes are all independently regulated despite their structural homology and tandem clustered organization. Two of the genes, pelA and pelE, encoded proteins that differed greatly in their isoelectric points and ability to macerate plant tissue. A recombinant gene constructed with the 5' portion of pelE and the 3' portion of pelA yielded a chimeric protein with high pectate lyase activity but relatively low maceration activity. This result raised the possibility that the poor maceration ability of the pelA gene product may involve other properties in addition to its low isoelectric point.