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Sulfur-regulated control of the met-2 + gene of Neurospora crassa encoding cystathionine β-lyase

Brad S Reveal and John V Paietta*

Author Affiliations

Department of Biochemistry and Molecular Biology, Wright State University, Dayton, OH 45435, USA

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BMC Research Notes 2013, 6:259  doi:10.1186/1756-0500-6-259

Published: 8 July 2013



Cystathionine β-lyase performs an essential role in the transsulfuration pathway by its primary reaction of forming homocysteine from cystathionine. Understanding how the Neurospora crassa met-2+ gene, which encodes cystathionine β-lyase, is regulated is important in determining the basis of the cellular control of transsulfuration. The aim of this study was to determine the nature of a potential regulatory connection of met-2+ to the Neurospora sulfur regulatory network.


The cystathionine β-lyase (met-2+) gene was cloned by the identification of a cosmid genomic clone capable of transforming a met-2 mutant to methionine prototrophy and subsequently characterized. The gene contains a single intron and encodes a protein of 457 amino acids with conserved residues predicted to be important for catalysis and pyridoxal-5′-phosphate co-factor binding. The expression of met-2+ in wild-type N. crassa increased 3.1-fold under sulfur-limiting growth conditions as compared to the transcript levels seen under high sulfur growth conditions (i.e., repressing conditions). In a Δcys-3 strain, met-2+ transcript levels were substantially reduced under either low- or high-sulfur growth conditions. In addition, the presence of CYS3 activator binding sites on the met-2+ promoter was demonstrated by gel mobility shift assays.


In this report, we demonstrate the sulfur-regulated expression of the met-2+ gene and confirm its connection to the N. crassa sulfur regulatory circuit by the reduced expression observed in a Δcys-3 mutant and the in vitro detection of CYS3 binding sites in the met-2+ promoter. The data further adds to our understanding of the regulatory dynamics of transsulfuration.

Cystathionine β-lyase; met-2+; Transsulfuration; Sulfur gene regulation; CYS3 regulator; Neurospora crassa