We therefore propose that CBP plays an important role in insulator function and suggest that the HAT activity of CBP regulates insulating activity in some instances.
Importantly, the results of the EMSA and ChIP experiments provide strong support for the idea that the requirement for Elba activity evident in the RNAi knockdowns reflects a direct role in insulating activity rather than indirect role.
In his letter, Mr. Walker said that if the accounting office failed to try to gain access to the records, any future administration "seeking to insulate its activities from oversight and public scrutiny could do so simply by assigning these activities to the vice president or a body under the White House's direct control".
Another novel finding is that CBP binds to many, if not most, insulators across the genome and regulates insulating activity through its HAT activity at a subset of these insulators.
Interestingly this study shows that CTCF, the first transcription factor found to have insulating activity [28] and enhancer blocking function [13], [14] in mammalian cells, binds to the 5'HS5 core region at both the primitive and definitive stages in erythroid cells in vivo.
For all three Elba proteins, RNAi knockdowns compromises the insulating activity of both pHS1×4 and the Elba multimer.
Our findings would also explain why the insulating activity of the Elba factor/Elba sequence is developmentally restricted.
Only one DNA binding activity, Elba, had a stage-specificity consistent with the insulating activity of pHS1 (Aoki et al., 2008).
Conversely, multimerizing the Elba recognition sequence is sufficient to confer early insulating activity (Aoki et al., 2008; see Figure 1 figure supplement 1).
At a subset of these, CBP may regulate insulating activity, measured as the ability to prevent repressive H3K27 methylation from spreading into adjacent chromatin.
