Stauffer G V, Brenchley J E
Genetics. 1978 Feb;88(2):221-33. doi: 10.1093/genetics/88.2.221.
In Salmonella typhimurium the glyA gene product, serine transhydroxymethylase (E.C. 2.1.2.1.; L-serine:tetrahydrofolate-5,10-hydroxymethyltransferase) is responsible for the interconversion of serine and glycine. This reaction also provides the cell with one-carbon units from the 5,10-methylene-tetrahydrofolate formed during glycine synthesis. Despite the importance of this enzyme, however, no mutants in which its regulation has been specificially altered have been isolated. To isolate such mutants, we have devised a selection procedure using a strain (glyA951) in which the serine transhydroxymethylase activity is reduced. When this enzyme is completely repressed, the mutant requires gylcine for growth. Revertants which retain the glyA951 lesion, but no longer require glycine, have been isolated and the serine transhydroxymethylase regulation examined. One revertant has a 7-fold elevated serine transhydroxymethylase level, which can be repressed the normal amount (about 5-fold) when the cells are grown in supplemented media. Another revertant has only a 2-fold higher serine transhydroxymethylase level; however, the amount of repression is reduced. The new lesions in both mutants cotransduce with the glyA gene and are distinct from other mutations that alter the regulation of both serine transhydroxymethylase and the methionine biosyntheitc enzymes.
在鼠伤寒沙门氏菌中，glyA基因产物丝氨酸转羟甲基酶（E.C. 2.1.2.1；L-丝氨酸：四氢叶酸-5,10-羟甲基转移酶）负责丝氨酸和甘氨酸的相互转化。该反应还为细胞提供了甘氨酸合成过程中形成的5,10-亚甲基四氢叶酸中的一碳单位。然而，尽管这种酶很重要，但尚未分离出其调控被特异性改变的突变体。为了分离此类突变体，我们设计了一种筛选程序，使用一种丝氨酸转羟甲基酶活性降低的菌株（glyA951）。当这种酶被完全抑制时，该突变体需要甘氨酸才能生长。我们已经分离出保留glyA951损伤但不再需要甘氨酸的回复突变体，并对丝氨酸转羟甲基酶的调控进行了检测。一个回复突变体的丝氨酸转羟甲基酶水平提高了7倍，当细胞在补充培养基中生长时，该水平可被抑制到正常水平（约5倍）。另一个回复突变体的丝氨酸转羟甲基酶水平仅高2倍；然而，抑制量减少了。这两个突变体中的新损伤都与glyA基因共转导，并且与其他改变丝氨酸转羟甲基酶和甲硫氨酸生物合成酶调控的突变不同。
