Kraemer K H, Seidman M M
Laboratory of Molecular Carcinogenesis, National Cancer Institute, Bethesda, MD 20892.
Mutat Res. 1989 Mar-May;220(2-3):61-72. doi: 10.1016/0165-1110(89)90011-0.
The Escherichia coli tyrosine amber suppressor tRNA gene, supF, has been utilized as a mutagenic target in several shuttle-vector plasmids. Data on mutagenic inactivation of suppressor activity was obtained from induced mutagenesis experiments with plasmids pZ189 and p3AC, and from studies on alterations of the supF gene transduced into E. coli. 162 single or tandem base-substitution mutations that reduce or eliminate suppressor activity were identified at 86 sites within 158 base pairs. The 2 transition and 4 transversion mutations possible in double-stranded DNA were all detectable. At 56 sites two different inactivating mutations were found; and at 20 sites all 3 possible base substitution mutations inactivated suppressor function. Most of the mutations were clustered within the mature tRNA region: 144 of the base-substitution mutations were found at 74 sites within the 85-bp mature tRNA region. Insertions of 1 or 2 bases at 4 sites and deletions of 1 to 3 bases at 15 sites were found to inactivate supF function. A few silent mutations which do not inactivate suppressor function were found: single base-substitutions at 4 sites, 14 pairs of silent double mutations, and a large deletion including the promoter region. The supF gene is thus an extremely sensitive target for mutagenic inactivation in shuttle-vector plasmids.
大肠杆菌酪氨酸琥珀抑制tRNA基因supF已被用作几种穿梭载体质粒的诱变靶点。关于抑制活性诱变失活的数据来自用质粒pZ189和p3AC进行的诱导诱变实验，以及对转导到大肠杆菌中的supF基因改变的研究。在158个碱基对中的86个位点鉴定出162个降低或消除抑制活性的单碱基或串联碱基取代突变。双链DNA中可能的2种转换突变和4种颠换突变均能被检测到。在56个位点发现了两种不同的失活突变；在20个位点所有3种可能的碱基取代突变均使抑制功能失活。大多数突变集中在成熟tRNA区域：85个碱基对的成熟tRNA区域内74个位点发现了144个碱基取代突变。在4个位点发现1或2个碱基的插入，在15个位点发现1至3个碱基的缺失可使supF功能失活。发现了一些不使抑制功能失活的沉默突变：4个位点的单碱基取代、14对沉默双突变以及包括启动子区域的大片段缺失。因此，supF基因是穿梭载体质粒诱变失活的一个极其敏感的靶点。
