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Junk DNA: Three speculations

Keith Robison robison at mito.harvard.edu
Mon Jul 24 10:30:41 EST 1995

John A. Baughman (jab at ix.netcom.com) wrote:
: 	First, let me state my baises: I'm much more familiar with the 
: information processing side of things that the nuts-and-bolts molecular
: biology, so I'm counting on you to keep me honest. I also realize that 
: to a person with a hammer everything looks like a nail. That said...
: 	1) Since nature endures little that is not immediately useful
: (and usually efficient), "junk" DNA is probably not much like "junk"

This isn't obviously true.  Nature doesn't always tolerate 
_paying a price_ for ineffiency -- in many biological systems
the cost of junk DNA may be so little that there is not pressure
to drive it out.

: It has been
: suggested that the "quartenary" or structural use has been for 
: positioning the strand. This is attractive, but seems weakened by the
: notion that the unused strand, in fact the major portion of the
: molecule,
: would have to maintained with the same vigor as the "live" part. The
: overhead would be high for that kind of return.
: 	2) On the other hand, the proximity of used sequences might make
: the strand vulnerable to mechanical breaking. Inert portions could
: insulate
: the events, and, since the bonding is both lateral (base pairs) and
: longitudinal (along the ribose spine) a cabling effect would occur.
: 	3) There has been speculation that the unused portions may be
: inactive, older versions of modern code. If this is the case
: functionally
: (but probably not structurally, see "2"), there might be some
: redundancy 
: at work. It might even permit some form of intra-genetic competition, 
: reducing the shock effects of some forms of mutation.
: 	I eagerly look forward to feedback on these speculations.

I suggest that before you go speculating on the function of the
"junk", you take a look at what it looks like.  And, as someone
suggested here, it would be helpful to look at the classic 
articles by Sapienza, Crick, and Doolittle on selfish DNA.

Keith Robison
Harvard University
Department of Cellular and Developmental Biology
Department of Genetics / HHMI

robison at mito.harvard.edu 

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