Multi-subunit SMC ATPases control chromosome superstructure and DNA topology, presumably by DNA translocation and loop extrusion. Chromosomal DNA is entrapped within the tripartite SMCkleisin ring. Juxtaposed SMC heads ("J heads") or engaged SMC heads ("E heads") split the SMCkleisin ring into "S" and "K" sub-compartments. Here, we map a DNA-binding interface to the S compartment of E heads SmcScpAB and show that head-DNA association is essential for efficient DNA translocation and for traversing highly transcribed genes in Bacillus subtilis. We demonstrate that in J heads, SmcScpAB chromosomal DNA resides in the K compartment but is absent from the S compartment. Our results imply that the DNA occupancy of the S compartment changes during the ATP hydrolysis cycle. We propose that DNA translocation involves DNA entry into and exit out of the S compartment, possibly by DNA transfer between compartments and DNA segment capture.

中文翻译：

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SMC臂间空间在原核凝聚素中的瞬时DNA占用。

多亚基SMC ATPases可能是通过DNA易位和环挤出来控制染色体的超结构和DNA拓扑结构。染色体DNA夹在三方SMCkleisin环内。并置的SMC头（“ J头”）或接合的SMC头（“ E头”）将SMCkleisin环分成“ S”和“ K”子隔间。在这里，我们将DNA结合界面映射到E头SmcScpAB的S区室，并显示头DNA关联对于有效的DNA移位和遍历枯草芽孢杆菌中高度转录的基因是必不可少的。我们证明，在J头中，SmcScpAB染色体DNA驻留在K区室中，但S区室中却不存在。我们的结果表明，在ATP水解循环中，S区的DNA占有率发生了变化。