Summary: Two pectinesterase-positive clones, differing in expression levels, were isolated from a genomic library of . Both clones contained a common DNA fragment which included the pectinesterase-encoding region. The different expression levels found with the two clones could be ascribed to different positioning of the pectinesterase gene with respect to a vector promoter. Restriction analysis, subcloning, and further exonuclease deletion mapping revealed that the genetic information for pectinesterase was located within a 1·3 kb fragment. A protein of 41 to 42 kDa was expressed from this fragment. Nucleotide sequence analysis of the respective region disclosed an open reading frame of 1188 bp. The deduced polypeptide had a calculated molecular mass of 41004 Da, which is consistent with the determined size of the pectinesterase protein. The predicted amino acid sequence showed significant homology to pectinesterases from and tomato. In cultures of clones up to 30% of total pectinesterase activity was transported into the medium. However, no significant pectinesterase activity could be detected in the periplasm.


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