Scheirer K E, Higgins N P
Department of Biochemistry and Molecular Genetics, University of Alabama at Birmingham, 861-A BBRB, 845 19th Street South, Birmingham, AL 35294, USA.
Biochimie. 2001 Feb;83(2):155-9. doi: 10.1016/s0300-9084(00)01215-3.
In enteric bacteria, chromosomes are partitioned into domains that exhibit restricted supercoil movement. The most common domain barrier detected by gammadelta resolution assays is random with respect to sequence and occurs more frequently in cells growing rapidly in rich medium compared to cells in stationary phase. Transcription generates both positive and negative supercoiling movement. To address the question of whether transcription causes the appearance of new domain boundaries, a transcriptionally active MudI element was substituted for a MudJr-1 element that resides within the cobT gene of Salmonella typhimurium. Mu-specific transcription from the phage early promoter was placed under control of either the wild type (c(+)) or the temperature-sensitive (cts62) repressor. Using a resolution assay with res sites at six chromosomal locations, domain structure was normal in cells carrying the MudAr-1 prophage with a wild type Mu repressor. However, in cells with a MudAr-1 prophage harboring the cts62 repressor, a new domain barrier appeared in > 90% of the cells. Supercoil movement was restricted ahead of but not behind the transcription machinery. We conclude that the strong Mu early promoter induces the appearance of a domain barrier within the limits of a MudAr-1 prophage.
在肠道细菌中，染色体被划分为显示受限超螺旋运动的结构域。通过γδ分辨率测定法检测到的最常见的结构域屏障在序列方面是随机的，并且与处于稳定期的细胞相比，在富含培养基中快速生长的细胞中更频繁地出现。转录产生正向和负向超螺旋运动。为了解决转录是否导致新的结构域边界出现的问题，将转录活性的MudI元件替换为位于鼠伤寒沙门氏菌cobT基因内的MudJr - 1元件。来自噬菌体早期启动子的Mu特异性转录置于野生型（c(+)）或温度敏感型（cts62）阻遏物的控制之下。使用在六个染色体位置具有res位点的分辨率测定法，携带带有野生型Mu阻遏物的MudAr - 1原噬菌体的细胞中的结构域结构正常。然而，在携带cts62阻遏物的MudAr - 1原噬菌体的细胞中，超过90%的细胞出现了新的结构域屏障。超螺旋运动在转录机器之前受到限制，但在转录机器之后不受限制。我们得出结论，强Mu早期启动子在MudAr - 1原噬菌体范围内诱导了结构域屏障的出现。
