Unusual synthesis by the Escherichia coli CCA-adding enzyme
Unusual synthesis by the Escherichia coli CCA-adding enzyme
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DOI：
10.1017/s1355838200000686
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发表时间：
2000-07-01
期刊：
影响因子：
4.5
通讯作者：
Hou, YM
中科院分区：
文献类型：
--
作者：
Hou, YM
tRNA的3'端在74-76位含有保守的CCA序列。CCA序列由CCA添加酶合成和维持。使用含有置换的3'末端的合成微螺旋底物研究了大肠杆菌酶在74-76个位置中的每一个的特异性。结果表明，该酶具有合成不寻常的3'末端的能力。当与CTP单独孵育时，酶催化添加C74、C75、C76和多个Cs。虽然C74和C75的加入如预期的那样，但C76和多种Cs的加入不是。特别是，添加C76产生了CCC，这与酶的生物学作用相冲突。然而，ATP的存在阻止了CCC的合成，并将特异性完全转换为CCA。ATP的存在也对多个Cs的合成有抑制作用。因此，E.大肠杆菌CCA酶可以是多聚（C）聚合酶，但其多聚（C）的合成受ATP的存在调节。这些特征导致CCA合成的模型是独立的核酸模板。通过CCA添加酶合成聚（C）使人联想到通过聚（A）聚合酶合成聚（A），并且它为核苷酸基转移酶家族中这两种酶之间的紧密序列关系提供了功能原理。
The tRNA 3' end contains the conserved CCA sequence at the 74-76 positions. The CCA sequence is synthesized and maintained by the CCA-adding enzymes. The specificity of the Escherichia coli enzyme at each of the 74-76 positions was investigated using synthetic minihelix substrates that contain permuted 3' ends. Results here indicate that the enzyme has the ability to synthesize unusual 3' ends. When incubated with CTP alone, the enzyme catalyzed the addition of C74, C75, C76, and multiple Cs. Although the addition of C74 and C75 was as expected, that of C76 and multiple Cs was not. In particular, the addition of C76 generated CCC, which would have conflicted with the biological role of the enzyme. However, the presence of ATP prevented the synthesis of CCC and completely switched the specificity to CCA. The presence of ATP also had an inhibitory effect on the synthesis of multiple Cs. Thus, the E. coli CCA enzyme can be a poly(C) polymerase but its synthesis of poly(C) is regulated by the presence of ATP. These features led to a model of CCA synthesis that is independent of a nucleic acid template. The synthesis of poly(C) by the CCA-adding enzyme is reminiscent of that of poly(A) by poly(A) polymerase and it provides a functional rationale for the close sequence relationship between these two enzymes in the family of nucleotidyltransferases.