Lau L F, Roberts J W, Wu R
Proc Natl Acad Sci U S A. 1982 Oct;79(20):6171-5. doi: 10.1073/pnas.79.20.6171.
Transcription of the rightward operon of bacteriophage lambda terminates in the presence of rho factor at a region known as tR1, located downstream of the structural gene for the lytic repressor cro. We demonstrate by nuclease Sl mapping that transcription termination at lambda tR1 occurs in vitro over a stretch of 60 nucleotides. End points of transcripts are clustered in three distinct regions, which we refer to as termination sites I, II, and III. Termination at site I is inhibited by L factor, whereas termination at sites II and III is not affected by L factor. The sensitivities of these sites to rho factor are in the order III greater than II greater than I. The cin-lcnc-l mutations abolish termination at site II but not at sites I and III; this result may explain the failure of these mutations to alleviate the phage requirement for N function for growth. Although possible stem-and-loop structures in the RNA transcript immediately upstream of each of the three termination sites can be found, no consistent correlation exists between the strengths of these stem-and-loop structures and the termination efficiencies of their respective sites.
噬菌体λ向右操纵子的转录在ρ因子存在的情况下，于一个名为tR1的区域终止，该区域位于裂解阻遏物cro的结构基因下游。我们通过核酸酶S1作图证明，λ tR1处的转录终止在体外发生在一段60个核苷酸的区域。转录本的端点聚集在三个不同的区域，我们将其称为终止位点I、II和III。位点I的终止受L因子抑制，而位点II和III的终止不受L因子影响。这些位点对ρ因子的敏感性顺序为III大于II大于I。cin-lcnc-1突变消除了位点II的终止，但不影响位点I和III的终止；这一结果可能解释了这些突变未能减轻噬菌体生长对N功能的需求的原因。尽管在三个终止位点中每个位点紧邻的RNA转录本中都可以找到可能的茎环结构，但这些茎环结构的强度与其各自位点的终止效率之间不存在一致的相关性。
