ABSTRACT
Ketopantoate hydroxymethyltransferase, which is encoded by the panB gene in the lower eukaryote Aspergillus nidulans, is essential for the biosynthesis of coenzyme A, while the pathway intermediate 4'-phosphopantetheine is required for penicillin production. Ketopantoate hydroxymethyltransferase could also serve as a target for anti-fungal drugs, since it is not present in mammals. Clones of panB were identified by complementation of the corresponding mutant, and the DNA sequence of the gene was determined. The fungal panB gene encodes a predicted protein of molecular mass 37.7 kDa, containing two short sequence motifs, LeuValGlyAspSer and GlyIleGlyAlaGly, that are completely conserved between prokaryotic and eukaryotic homologues. The mutation panB100 was found to result in deletion of Gly-168, the last glycine within the latter conserved motif. Analysis by gel filtration suggests that the fungal PanB protein can be expressed in Escherichia coli as an active octameric enzyme. The panB transcript is present in low abundance and, most probably, a small increase in transcript levels occurs in the absence of exogenous pantothenate.
