Nonlinearity in genetic decoding: Homologous DNA replicase genes use alternatives of transcriptional slippage or translational frameshifting
Nonlinearity in genetic decoding: Homologous DNA replicase genes use alternatives of transcriptional slippage or translational frameshifting
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DOI：
10.1073/pnas.97.4.1683
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发表时间：
2000-02-15
影响因子：
11.1
通讯作者：
Gesteland, RF
中科院分区：
文献类型：
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作者：
Larsen, B;Wills, NM;Gesteland, RF
DNA 聚合酶 III 的 tau 和 γ 亚基均由大肠杆菌和嗜热栖热菌中的单个基因编码。 gamma 的大小是 tau 的三分之二，几乎与 tau 共享其所有氨基酸序列，大肠杆菌和嗜热嗜热链球菌已经进化出非常不同的机制来设置 tau 和 gamma 之间大约 1:1 的比例。这两种机制都将核糖体放入替代阅读框中，以便新框架中的终止密码子用于制造更小的 γ 蛋白。在大肠杆菌中，大约 50% 的起始核糖体按照常规方式翻译 dnaX mRNA 以产生 tau，但另外 50% 的起始核糖体在 mRNA 的特定位点 (A AAA AAG) 处转换至 -1 阅读框以产生 γ。在嗜热嗜热菌中，不需要核糖体移码：dnaX mRNA 是异质分子群体，具有不同数量的 A 残基，这些 A 残基是由 DNA 模板中九个 T 残基的转录滑移产生的。包含 9 个 As（或 +/- 3 个 As 的倍数）的亚群的翻译产生 tau。其余 mRNA 群体（包含 9 个 +/- 3 个 As 的非倍数）将核糖体放入替代阅读框中以产生 γ 蛋白。令人惊讶的是，大肠杆菌和嗜热链球菌中两个相当相似的 dnaX 序列导致了非常不同的表达机制。
The tau and gamma subunits of DNA polymerase III are both encoded by a single gene in Escherichia coli and Thermus thermophilus. gamma is two-thirds the size of tau and shares virtually all its amino acid sequence with tau, E. coli and T. thermophilus have evolved very different mechanisms for setting the approximate 1:1 ratio between tau and gamma, Both mechanisms put ribosomes into alternate reading frames so that stop codons in the new frame serve to make the smaller gamma protein. In E, coli, approximate to 50% of initiating ribosomes translate the dnaX mRNA conventionally to give tau, but the other 50% shift into the -1 reading frame at a specific site (A AAA AAG) in the mRNA to produce gamma. In T. thermophilus ribosomal frameshifting is not required: the dnaX mRNA is a heterogeneous population of molecules with different numbers of A residues arising from transcriptional slippage on a run of nine T residues in the DNA template. Translation of the subpopulation containing nine As (or +/- multiples of three As) yields tau. The rest of the population of mRNAs (containing nine +/- nonmultiples of three As) puts ribosomes into the alternate reading frames to produce the gamma protein(s). It is surprising that two rather similar dnaX sequences in E. coli and T. thermophilus lead to very different mechanisms of expression.