Demonstration of UDP-glucose dehydrogenase activity in cell extracts of Escherichia coli expressing the pneumococcal cap3A gene required for the synthesis of type 3 capsular polysaccharide

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Abstract
The gene cluster of Streptococcus pneumoniae coding for the type 3 capsular polysaccharide contains four genes (cap3ABCD). A DNA fragment containing the cap3A gene was amplified by PCR and cloned under the control of a T7 RNA polymerase-dependent promoter. Overexpression of this gene in Escherichia coli resulted both in a 47-kDa protein in the cytoplasm of isopropyl-beta-D-thiogalactopyranoside-induced bacteria and in high levels of UDP-glucose dehydrogenase activity. These data demonstrate, in a direct experimental way, that cap3A encodes the UDP-glucose dehydrogenase of pneumococcus type 3.