Natural Science Forum / Biology / Microbiology / January 2007

Well, at the simplest level, it means that a particular site is hit
more often by the nuclease than other sites. For _hyper_sensitive,
_much_ more often.

Note that these measurements are made with chromatin, not with free
DNA. (Also, they could be made with artificial protein-DNA complexes
of interest.) Further, they are made under conditions where
(idealized) only one nuclease hit occurs per molecule, So the
distribution of fragment sizes is a measure of the sites that were
hit. If the DNA were uniformly sensitive along its length, then one
would get a smooth distribution of fragment lengths.

Sites that are more sensitive are somehow more exposed -- probably due
to some combination of not being covered with protein and being bent
in a way to expose certain sites. Some authors distinguish sensitive
and hypersensitive sites. The latter often correlate with control
regions.

bob