Posted: May 18, 2014 6:39 pm
by GenesForLife
DavidMcC wrote:
GenesForLife wrote:
AFAIK, the main category of "junk DNA" refers to sequences that make up the chromatin "packaging" that wraps round the actual genes most of the time.


Nope -

[1] DNA alone never makes up chromatin packaging.
[2] Chromatin consists of histones in combination with DNA.
...

Ha! A classic case of interpretation issues. The fact that the chromatin includes DNA is sufficient to make my arguent valid.



Piffle. You don't get chromatin that contains junk DNA wrapping around genic DNA to regulate it. PPS - chromatin doesn't wrap round DNA either, DNA is wrapped around histones and the entirety, which is called chromatin, is either compacted or not.


[3] Heterochromatin (which is highly compacted and wraps around silent DNA) does not wrap around genes.

Fair enough, but it doesn't invalidate my argument that much "junk DNA" has a function - one of suppressing accidental gene expression.


Junk DNA does not suppress accidental gene expression - histone marks in genic chromatin are sufficient to model gene expression and does not need the invocation of heterochromatin being wrapped round gene as a determinant. Activatory and repressive histone marks DO NOT depend on junk DNA to be established. I should have been more precise - heterochromatin doesn't wrap around silent DNA, heterochromatin is made of silent DNA in combination with histones carrying exclusively repressive histone marks.

Reference for predictive modelling of gene expression from histone mark profiles http://genomebiology.com/2012/13/9/r53