Aspergillus nidulans genes encoding reverse transsulfuration enzymes belong to homocysteine regulon
- 170 Downloads
Homocysteine is an intermediate in methionine synthesis in Aspergillus nidulans, but it can also be converted to cysteine by the reverse transsulfuration pathway involving cystathionine β-synthase (CBS) and cystathionine γ-lyase (CGL). Because homocysteine is toxic to the cell at high concentrations, this pathway also functions as a means of removal of its excess. We found that the transcription of the mecA and mecB genes encoding CBS and CGL was upregulated by excess of homocysteine as well as by shortage of cysteine. Homocysteine induced transcription of both genes when added to the growth medium or overproduced in a regulatory mutant. The derepressing effect of cysteine shortage was observed in some mutants and in the wild-type strain during sulfur starvation. An increase in the level of mecA or mecB transcript roughly parallel with the elevation of the respective enzyme activity. On the basis of the mode of mecA and mecB regulation by homocysteine, these genes may be classified in a group of genes upregulated directly or indirectly by this amino acid. We call this group of genes the “homocysteine regulon”.
KeywordsAspergillus nidulans Transsulfuration Cystathionine β-synthase Cystathionine γ-lyase Regulation by homocysteine
We thank Drs. B. A. Roe, D. Kupfer, H. Zhu, J. Gray, S. Clifton, R. Prade, J. Loros, J. Dunlap and M. Nelson for the information supplied by the Aspergillus nidulans and the Neurospora crassa cDNA Sequencing Project at the Whitehead Institute/MIT Center. This work was supported by the State Committee for Scientific Research (grant no. 2P04A04628) to A. P.
- Chomczynski P (1993) A reagent for the single-step simultaneous isolation of RNA, DNA and proteins from cell and tissue samples. Biotechniques 15:532–534; 536–537Google Scholar
- Piotrowska M, Paszewski A (1986) Propargylglycine as a fungal inhibitor: effect on sulphur amino acid metabolism. J Gen Microbiol 132:2753–2760Google Scholar
- Sambrook J, Fritsch EF, Maniatis T (1989) Molecular cloning: a laboratory manual, 2nd edn. Cold Spring Harbor Laboratory Press, Cold Spring Harbor, p 1659Google Scholar
- Wróbel M, Lewandowska I, Bronowicka-Adamska P, Paszewski A (2008) The level of sulfane sulfur in the fungus Aspergillus nidulans wild type and mutant strains. Amino acids. doi: 10.1007/s00726-008-0175-x