Cesium Chloride Density purification before IP - (Jun/30/2005 )

Hi all, could someone tell me why is it that some protocols call for CsCl density purification of the chromatin before IP and some donot? I plan to look at certain transcription factors and also histone modifications under different conditions on the VEGF promoter. What would I gain (if any) by doing a CsCl gradient purification? By omitting this step, I can actually cut down on two days but at the same time I need to have very clear background for my experiment.
Thanks for your help.

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hi,
§What would I gain (if any) by doing a CsCl gradient purification?

In fly ChIP, classical protocol, calls for CsCl density purification; most other organism ChIPs not.

logically,it seems , CsCl gradient purification can better collect homogenized chromatin fragments ?!

However, in one latest MCB paper, the authors see some bias in this step so that in some material
system errors seem be introduced in ChIP.

Therefore it might be better to omit this step, at least in non-fly* ChIP.

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