Gourse R L, Stark M J, Dahlberg A E
Cell. 1983 Apr;32(4):1347-54. doi: 10.1016/0092-8674(83)90315-x.
We have examined the transcription of two plasmid-encoded, stable RNAs; a shortened 16S ribosomal RNA and the spacer transfer RNA2Glu from the Escherichia coli rrnB operon. Plasmid deletions were constructed in vitro, in order to examine the DNA regions required for stringent control of rRNA expression in vivo during amino acid starvation. We find that rRNA synthesized from plasmids does exhibit a relA-dependent, stringent response. The DNA sequences required for this regulation do not extend beyond 20 bases downstream of the P1 transcription initiation site. Deletion of P2, the second of the two tandem rRNA promoters, does not weaken the stringent control of transcripts from P1. These results demonstrate that pause sites for RNA polymerase identified in vitro do not play a significant role in the stringent control of rRNA synthesis in vivo and imply that stringent regulation takes place at the level of initiation, rather than elongation, of transcription. Surprisingly, we find that the presence of extra intact rrnB operons (carried by a multicopy plasmid) reduces the magnitude of the stringent response.
我们研究了两种质粒编码的稳定RNA的转录情况，即来自大肠杆菌rrnB操纵子的缩短型16S核糖体RNA和间隔区转移RNA2Glu。为了研究在氨基酸饥饿期间体内严格控制rRNA表达所需的DNA区域，我们在体外构建了质粒缺失体。我们发现，从质粒合成的rRNA确实表现出依赖relA的严格反应。这种调控所需的DNA序列不会延伸到P1转录起始位点下游20个碱基以外。两个串联rRNA启动子中的第二个P2的缺失，并不会削弱对来自P1的转录本的严格控制。这些结果表明，体外鉴定出的RNA聚合酶暂停位点在体内rRNA合成的严格控制中并不起重要作用，这意味着严格调控发生在转录起始水平，而非延伸水平。令人惊讶的是，我们发现额外完整的rrnB操纵子（由多拷贝质粒携带）的存在会降低严格反应的幅度。
