Cherest H, Surdin-Kerjan Y
Laboratoire d'Enzymologie du C.N.R.S., Gif-sur-Yvette, France.
Genetics. 1992 Jan;130(1):51-8. doi: 10.1093/genetics/130.1.51.
We have identified a mutation in a gene of Saccharomyces cerevisiae, STR1, that leads to a strict nutritional requirement for cysteine. The str1-1 mutation decreases to an undetectable level the cystathionine gamma-lyase activity. This enzyme catalyzes one of the two reactions involved in the transsulfuration pathway that yields cysteine from homocysteine with the intermediary formation of cystathionine. The phenotype induced by this mutation implies that, in S. cerevisiae, the sulfur atom of sulfide resulting from the reductive assimilation of sulfate is incorporated into a four carbon backbone yielding homocysteine, which, in turn, is the precursor of the biosynthesis of both cysteine and methionine. This also reveals that the direct synthesis of cysteine by incorporation of the sulfur atom into a three carbon backbone as found in Escherichia coli does not occur in S. cerevisiae. The study of the meiotic progeny of diploid strains heterozygous at the STR1 locus has shown that the str1-1 mutation undergoes a particularly high frequency of meiotic gene conversion.
我们在酿酒酵母的一个基因STR1中鉴定出了一个突变，该突变导致对半胱氨酸有严格的营养需求。str1-1突变将胱硫醚γ-裂合酶活性降低到无法检测的水平。这种酶催化转硫途径中两个反应之一，该途径以胱硫醚为中间产物，从同型半胱氨酸生成半胱氨酸。此突变诱导的表型表明，在酿酒酵母中，由硫酸盐还原同化产生的硫化物中的硫原子被整合到一个四碳骨架中生成同型半胱氨酸，而后者又是半胱氨酸和甲硫氨酸生物合成的前体。这也表明，酿酒酵母中不像大肠杆菌那样通过将硫原子整合到一个三碳骨架中来直接合成半胱氨酸。对STR1位点杂合的二倍体菌株减数分裂后代的研究表明，str1-1突变在减数分裂基因转换中发生的频率特别高。
