Sieńko M, Topczewski J, Paszewski A
Institute of Biochemistry and Biophysics, Polish Academy of Sciences, Pawi'nskiego 5a, 02-106 Warsaw, Poland.
Curr Genet. 1998 Feb;33(2):136-44. doi: 10.1007/s002940050319.
The A. nidulans cysD gene encoding homocysteine synthase (O-acetyl-L-homoserine sulphydrylase) has been isolated by functional complementation of a cysD11 mutation. The gene contains five short introns and codes for a protein of 437 amino acids. The protein shows homology with bacterial and yeast O-acetyl- and O-succinyl-homoserine sulphydrylases, particularly from Schizosaccharomyces pombe, Saccharomyces cerevisiae and Kluyveromyces lactis. The cysD cDNA is able to complement a S. cerevisiae mutation impairing homocysteine synthase. Synthesis of the cysD mRNA is down-regulated by a high concentration of methionine in growth medium without sulphate and up-regulated under sulphur limitation. A comparison of cysD genomic and cDNA copies, derived from different A. nidulans strains, revealed a marked DNA-sequence polymorphism manifested mostly by silent point mutations. There was, however, much less polymorphism in the protein sequence.
通过对cysD11突变进行功能互补，分离出了构巢曲霉中编码高半胱氨酸合酶（O-乙酰-L-高丝氨酸巯基化酶）的cysD基因。该基因含有5个短内含子，编码一个由437个氨基酸组成的蛋白质。该蛋白质与细菌和酵母的O-乙酰-和O-琥珀酰-高丝氨酸巯基化酶具有同源性，特别是与粟酒裂殖酵母、酿酒酵母和乳酸克鲁维酵母的同源性较高。cysD cDNA能够互补酿酒酵母中损害高半胱氨酸合酶的突变。在无硫酸盐的生长培养基中，高浓度的甲硫氨酸会下调cysD mRNA的合成，而在硫限制条件下则会上调。对来自不同构巢曲霉菌株的cysD基因组和cDNA拷贝进行比较，发现存在明显的DNA序列多态性，主要表现为沉默点突变。然而，蛋白质序列中的多态性要少得多。
