Kim Steven J, Martinson Harold G
Department of Chemistry and Biochemistry, University of California at Los Angeles, Los Angeles, CA 90095-1569, USA.
J Biol Chem. 2003 Oct 24;278(43):41691-701. doi: 10.1074/jbc.M306304200. Epub 2003 Aug 21.
Genes encoding polyadenylated mRNAs depend on their poly(A) signals for termination of transcription. An unsolved problem is how the poly(A) signal triggers the polymerase to terminate. A popular model is that this occurs during extrusion of the poly(A) signal, at which time it interacts with factors on the transcription complex. To test this idea we used cis-antisense inhibition in vivo to probe the temporal relationship between poly(A) signal extrusion and the commitment of the polymerase to terminate. Our rationale was to inactivate the poly(A) signal at increasing times post-extrusion to determine the point beyond which it is no longer required for termination. We found that communication with the polymerase is not temporally restricted to the time of poly(A) signal extrusion, but is ongoing and perhaps random. Some polymerases terminate almost immediately. Others have yet to receive their termination instructions from the poly(A) signal even 500 bp downstream, as indicated by the ability of an antisense at this distance to block termination. Thus, the poly(A) signal can functionally interact with the polymerase at considerable distances down the template. This is consistent with the emerging picture of a processing apparatus that assembles and matures while riding with the polymerase.
编码聚腺苷酸化mRNA的基因依赖其聚腺苷酸化信号来终止转录。一个尚未解决的问题是聚腺苷酸化信号如何触发聚合酶终止转录。一个流行的模型认为，这发生在聚腺苷酸化信号挤出过程中，此时它与转录复合物上的因子相互作用。为了验证这一观点，我们在体内使用顺式反义抑制来探究聚腺苷酸化信号挤出与聚合酶终止转录的时间关系。我们的理论依据是在挤出后不同时间使聚腺苷酸化信号失活，以确定终止转录不再需要该信号的时间点。我们发现与聚合酶的通讯在时间上并不局限于聚腺苷酸化信号挤出的时刻，而是持续进行且可能是随机的。一些聚合酶几乎立即终止转录。另一些聚合酶即使在下游500 bp处，仍未收到来自聚腺苷酸化信号的终止指令，这可通过该距离处的反义核酸能够阻断终止转录得以证明。因此，聚腺苷酸化信号能够在模板下游相当远的距离与聚合酶发生功能性相互作用。这与转录加工装置在随聚合酶移动过程中组装并成熟的新观点是一致的。
