MOLECULAR-CLONING OF THE GTP-CYCLOHYDROLASE STRUCTURAL GENE RIB1 OF PICHIA-GUILLIERMONDII INVOLVED IN RIBOFLAVIN BIOSYNTHESIS

The structural gene of GTP-cyclohydrolase, involved in riboflavin biosynthesis, was cloned from a Pichia guilliermondii genomic library. A 1855 bp genomic DNA fragment complementing the riboflavin auxotrophies of an Escherichia coli ribA mutant, defective in GTP-cyclohydrolase II, and a P. guilliermondii rib1 mutant was isolated and sequenced. An open reading frame with the potential to encode a protein of 344 amino acids with a predicted molecular mass of 38 711 Da was detected. The P. guilliermondii enzyme shows a high degree of homology to GTP-cyclohydrolases type II from E. coli and Baccillus subtilis and to GTP-cyclohydrolase from Saccharomyces cerevisiae. Functional GTP-cyclohydrolase from P. guilliermondii may consist of four identical subunits. The sequence of the RIB1 gene of P. guilliermondii was submitted to the EMBL sequence database and is accessible under Accession Number Z49093.