One reason why DNAs are not entrapped in J S

One reason why DNAs are not entrapped in J-S compartments is that the coiled coils associated with the Smc1 and Smc3 heads are juxtaposed throughout their length, as suggested for bacterial Smc and eukaryotic cohesin (Bürmann et al., 2019, Diebold-Durand et al., 2017, Kulemzina et al., 2016). Lack of DNA entrapment in E-S compartments is more surprising given that it is widely assumed (by analogy with Rad50) that ATP-driven head engagement creates a DNA-binding groove that would be situated within the E-S compartment (Liu et al., 2016, Rojowska et al., 2014, Schüler and Sjögren, 2016, Seifert et al., 2016). If such a groove is also a feature of the E state in cohesin, then DNA binding at this site must be infrequent but could nevertheless be an important, albeit transient, event during the process of DNA entrapment. Alternatively, DNAs might lie within the groove as part of a loop (i.e., passage of DNA through the hole twice, once in one direction and once in the opposite), which would not result in S compartment entrapment as measured in our assay. Though our experiments shed important insight into the eventual location of sister DNAs within the cohesin ring, future experiments will be required to explore the series of events that create this state, in particular whether a fleeting entrapment within E-S compartments is involved, how DNAs enter cohesin rings, and how sister DNAs enter the same J-K compartment. Lastly, the topology of cohesin’s association with DNA when extruding loops also remains to be explored.
from:http://www.glpbio.com/