The metG gene of Aspergillus nidulans encoding cystathionine b-lyase: cloning and analysis

Abstract

The metG gene of Aspergillus nidulans encoding cystathionine β-lyase, an enzyme of the main pathway of methionine synthesis, was cloned by complementation of a metG mutation. A comparison of metG genomic DNA and a cDNA copy derived from different A. nidulans strains revealed a marked DNA sequence polymorphism manifested mostly by silent point mutations. cDNA of the A. nidulans metG gene complemented the Escherichia coli metC69 mutation impairing cystathionine β-lyase. This gene contains two introns and codes for a protein of 439 amino acids. The protein shows homology with bacterial, yeast and plant cystathionine β-lyases, as well as with other enzymes belonging to a large family of pyridoxal 5′-phosphate binding proteins. Transcription of the metG gene is not appreciably regulated by the concentration of sulphur source in the growth medium.