CTCF induces histone variant incorporation, erases the H3K27me3 histone mark and opens chromatin.
Bottom Line: The insulator factor, CTCF, has been found to bind to boundaries and to mediate insulator function.This demonstrates the causal role for CTCF in generating the chromatin features found at insulators.Thereby, spreading of a histone modification from one domain through the insulator into the neighbouring domain is inhibited.
Affiliation: Institute for Genetics, Justus-Liebig-University, 35392 Giessen, Germany.Show MeSH
Mentions: To determine the sequence of the molecular events of H3K27me3 removal and of chromatin domain opening we needed to determine the time required to establish these changes. We could not simply use different time points after transfection to do so, since expression of the fusion proteins takes time and has to be distinguished from the time after DNA binding. Therefore, again, we made use of the IPTG substance to interfere with DNA binding of the GFP-LacI-CTCF fusion. Removal of IPTG allows for DNA binding and, therefore, the time after DNA-binding required to induce the molecular changes at the chromatin array can be determined. The size of the LacO array did not change significantly immediately after IPTG removal and for up to 2 h of GFP-LacI-CTCF binding (Figure 6B an E). However, at 4 h the array size started to increase and continued to do so up to 40 h (Figure 6C–E). Longer incubations did not further increase the size of the array (not shown), and as such the major changes in domain opening are observed between 4 and 40 h of LacO binding of CTCF.
Affiliation: Institute for Genetics, Justus-Liebig-University, 35392 Giessen, Germany.