SummaryThe pathways of pectin and galacturonate catabolism InErwinia chrysanthemlconverge to form a common intermediate, 2‐keto‐3‐deoxygluconate, which is phosphorylated to form 2‐keto‐3‐deoxy‐6‐phospho‐giuconate (KDGP) and then cleaved by the aldolase encoded by thekdgAgene. We cloned thekdgAgene of theE. chrysanthemistrain 3937 by complementing anEscherichia coli kdgAmutation, using an RP4‐derivative plasm id. Restriction mapping of thekdgAregion and isolation ofkdgA‐lacfusions allowed the more precise localization of thekdgAgene and determination of its transcriptional direction. The nucleotide sequence of thekdgAregion indicated that thekdgAreading frame is 639 bases long, corresponding to a protein of 213 amino acids with a molecular mass of 22187 Da. Comparison of the deduced primary amino acid sequences of theE. chrysanthemiKDGP‐aldolase to theE. coli, Zymomonas mobilisandPseudomonas putidaenzymes showed that they are highly conserved. TheE. chrysanthemi kdgAstructural gene begins 153 bases downstream of an open reading frame that has a high homology with thezwf E. coligene encoding giucose‐6‐phosphate dehydrogenase. Thezwfgene is also linked toeda (kdgA)inE. coliandP. putidabut genetic organization is different. Regulation ofzwfandkdgAexpression inE. chrysanthemi wasanalysed usinglacZfusions. The expression ofzwfis independent of the growth rate, but is repressed in the presence of glucose. Induction ofkdgAby pectin‐degradation products is mediatedin vivoby the negative regulatory genekdgR, which also controls all the steps of pectin degradation. However, the KdgR repressor is unable to bindin vitroto the 5′