Cloning and sequencing of the 3-phosphoglycerate kinase (PGK) gene from Penicillium citrinum and its application to heterologous gene expression

The gene coding for 3-phosphoglycerate kinase (PGK) in ML-236B (compactin)-producing Penicillium citrinum was isolated from the recombinant phage lambda library using the corresponding Aspergillus nidulans pgk gene as a probe. The P. citrinum pgk gene has an open reading frame of 1,254 bp, encoding a protein of 417 amino acids with a predicted molecular weight of 44,079 daltons. The position of the two introns, 59 and 60 bp respectively, was deduced from an homology comparison with the sequence of the A. nidulans pgk gene. The PGK protein of P. citrinum shows extensive high homology to the PGKs of four other fungi: P. chrysogenum (93%), A. nidulans (84%), Trichoderma reesei (78%) and Saccharomyces cerevisiae (68%). Almost total conservation is found in P. citrinum of residues thought to be important for the structure and function of the yeast enzyme. The strong codon preference found has greater similarity to that in other filamentous fungi than in yeast. A DNA fragment encompassing the pgk gene was shown to hybridize a 1.35-kb poly(A)⁺RNA, sufficient to encode the PGK polypeptide. A fused gene, pgk-hpt, containing the putative pgk promoter and the open reading frame of the Escherichia coli hygromycin B phospho-transferase (hpt) gene was constructed, and was successfully used to transform P. citrinum to a hygromycin B (HmB)-resistant phenotype.