Labhart P, Reeder R H
Mol Cell Biol. 1987 May;7(5):1900-5. doi: 10.1128/mcb.7.5.1900-1905.1987.
rRNA transcription in Xenopus laevis terminates near a 7-base-pair (bp) conserved sequence (T3 box) located 200 bp upstream of the site of transcription initiation for the adjacent gene promoter. We present evidence here that a 12-bp element containing the T3 box is an essential part of the terminator. Using an oocyte injection assay, we found that the 12-bp element (but not the T3 box alone) severely reduced the amount of RNA detectable at sites downstream from itself and that the T3 box within the 12-bp element was required to specify the formation of correct 3' ends. This requirement for the 12-bp element was also seen in pulse-label experiments by using a homogenate of oocyte nuclei, but the present data did not allow us to determine the exact mechanism by which the 12-bp element acts. Removal of the T3 region from its normal location allowed a significant amount of readthrough transcripts to accumulate, indicating that additional sequences may be required for complete terminator function.
非洲爪蟾的核糖体RNA（rRNA）转录在一个位于相邻基因启动子转录起始位点上游200碱基对（bp）处的7碱基对（bp）保守序列（T3框）附近终止。我们在此提供证据表明，一个包含T3框的12碱基对元件是终止子的重要组成部分。通过卵母细胞注射试验，我们发现12碱基对元件（而非单独的T3框）会严重减少其自身下游位点可检测到的RNA量，并且12碱基对元件中的T3框是确定正确3'末端形成所必需的。在使用卵母细胞核匀浆进行的脉冲标记实验中也观察到了对12碱基对元件的这种需求，但目前的数据使我们无法确定12碱基对元件发挥作用的确切机制。将T3区域从其正常位置移除会导致大量通读转录本积累，这表明完整的终止子功能可能还需要其他序列。
