Weinrauch Y, Lacks S A
Mol Gen Genet. 1981;183(1):7-12. doi: 10.1007/BF00270130.
Maltose-negative mutations in the amylomaltase gene of Streptococcus pneumoniae were examined for the presence of nonsense mutations. Out of 28 single-site mutants tested, 3 were shown to be suppressible by an amber suppressor previously found by Gasc et al. (1979). In the presence of the suppressor these mutants manifested 10--30% of wild type amylomaltase activity. In addition to the amylomaltase governed by malM, and the maltosaccharide phosphorylase governed by malP (which maps to the side of malM distal to the regulatory gene, malR), a new maltose-inducible protein, governed by another gene, malX, was observed in gel electrophoretic patterns. The malX gene maps on the side of malM proximal to the malR gene. The approximate molecular weights of the amylomaltase, phosphorylase and malX polypeptides are 62,000, 87,000 and 50,000, respectively. There appear to be no polar effects of the nonsense mutations in the malM gene on synthesis of the gene products of either malP or malX. In a search for nonsense mutants at other loci, one was found in the end gene, which governs the major endonuclease, a membrane enzyme. None were detected among 5 mismatch-repair defective hex mutants analyzed.
对肺炎链球菌淀粉麦芽糖酶基因中的麦芽糖阴性突变进行了无义突变检测。在测试的28个单点突变体中，有3个被加斯克等人（1979年）之前发现的琥珀抑制子所抑制。在该抑制子存在的情况下，这些突变体表现出野生型淀粉麦芽糖酶活性的10%至30%。除了由malM控制的淀粉麦芽糖酶和由malP控制的麦芽糖磷酸化酶（其定位于malM远离调节基因malR的一侧）外，在凝胶电泳图谱中还观察到一种由另一个基因malX控制的新的麦芽糖诱导蛋白。malX基因定位于malM靠近malR基因的一侧。淀粉麦芽糖酶、磷酸化酶和malX多肽的近似分子量分别为62,000、87,000和50,000。malM基因中的无义突变似乎对malP或malX的基因产物合成没有极性影响。在寻找其他位点的无义突变体时，在控制主要内切核酸酶（一种膜酶）的末端基因中发现了一个。在分析的5个错配修复缺陷型hex突变体中未检测到无义突变体。
