Moskaleva N D, Sukhodolets V V
Genetika. 1981;17(9):1606-17.
From the Escherichia coli thymine auxotroph carrying a constitutive mutation for deo-enzymes (thy deoR) mutants (tpp38, tpp39 and tpp40) for thymidine phosphorylase (catalyzing a conversion of thymine to thymidine) were isolated via selection for a low thymine requirement. In the thy deoR+ genome these mutations led to inability of bacteria to use thymidine as the sole carbon source for growth, though the ability to utilize thymine was retained at the level comparable to that of thy deoR+ tpp+ bacteria. In the thy deoR genome mutations obtained led to a more efficient utilization of thymine in comparison with the thy deoR tpp++ strain. At the same time, the thymidine phosphorylase activity, as determined by a degradation of thymidine in bacterial extracts was lower in thy deoR strains carrying tpp38, tpp39 and tpp40 by factors 5,25 and 22, respectively, in comparison with the thy deoR tpp+ strain. The mutations tpp38, 39, 40 were localized in the distal part of the tpp structural gene (tpp39 and tpp40 being in the extreme distal position), whereas the earlier described tpp-leaky mutants incapable of using exogenous thymine for growth were mapped in the extreme proximal part of the tpp gene (Sukhodolets et al., 1971). It is proposed that the tpp-leaky mutations obtained enhance the thymidine phosphorylase affinity to deoxyribose-1-phosphate, a product in a reversible reaction of the thymidine phosphorolysis.
从携带脱氨酶组成型突变的大肠杆菌胸腺嘧啶营养缺陷型（thy deoR）中，通过选择低胸腺嘧啶需求，分离出胸苷磷酸化酶（催化胸腺嘧啶转化为胸苷）的突变体（tpp38、tpp39和tpp40）。在thy deoR +基因组中，这些突变导致细菌无法将胸苷作为唯一碳源用于生长，尽管利用胸腺嘧啶的能力保持在与thy deoR + tpp +细菌相当的水平。在thy deoR基因组中获得的突变导致与thy deoR tpp ++菌株相比，胸腺嘧啶的利用效率更高。同时，与thy deoR tpp +菌株相比，携带tpp38、tpp39和tpp40的thy deoR菌株中，通过细菌提取物中胸苷降解测定的胸苷磷酸化酶活性分别降低了5倍、25倍和22倍。突变tpp38、39、40位于tpp结构基因的远端部分（tpp39和tpp40处于最远端位置），而早期描述的无法利用外源胸腺嘧啶生长的tpp渗漏突变体则定位在tpp基因的最近端部分（Sukhodolets等人，1971年）。有人提出，获得的tpp渗漏突变增强了胸苷磷酸化酶对脱氧核糖-1-磷酸的亲和力，脱氧核糖-1-磷酸是胸苷磷酸解可逆反应中的一种产物。
