Chu W M, Ballard R E, Schmid C W
Section of Molecular and Cellular Biology, University of California, Davis, CA 95616, USA.
Nucleic Acids Res. 1997 Jun 1;25(11):2077-82. doi: 10.1093/nar/25.11.2077.
Four consecutive T residues in the sense strand are sufficient to terminate transcription by RNA polymerase III (pol III). Previously we observed that compared with this minimally sufficient terminator, five T residues immediately preceded by a palindromic sequence increases transcriptional expression both in vitro and in vivo, raising the question of whether a palindromic sequence has a role in pol III termination. Here we observe that site-directed mutations which eliminate the dyad symmetry of the palindromic sequence decrease transcriptional expression. Similar effects are observed whether dyad symmetry is eliminated in regions of the palindrome which are proximal or distal with respect to the terminator. Compensatory mutations at either site to restore dyad symmetry rescue transcriptional activity. These observations suggest that a higher order structure, such as a RNA hairpin, immediately preceding the terminator increases pol III transcriptional activity.
有义链上连续的四个T残基足以终止RNA聚合酶III（pol III）的转录。此前我们观察到，与这个最低限度的终止子相比，在回文序列之前紧邻五个T残基会在体外和体内都增加转录表达，这就引发了一个问题，即回文序列在pol III终止过程中是否发挥作用。在这里我们观察到，消除回文序列二元对称性的定点突变会降低转录表达。无论回文序列中相对于终止子近端或远端的区域消除二元对称性，都会观察到类似的效果。在任一位置进行补偿性突变以恢复二元对称性可挽救转录活性。这些观察结果表明，紧邻终止子的更高阶结构，如RNA发夹，会增加pol III的转录活性。
