Path: utzoo!attcan!uunet!lll-winken!lll-tis!ames!ncar!gatech!bloom-beacon!athena.mit.edu!ayermish
From: ayermish@athena.mit.edu (Aimee Yermish)
Newsgroups: sci.bio
Subject: Re: DNA for interstellar messages
Keywords: multiple protein coding
Message-ID: <6208@bloom-beacon.MIT.EDU>
Date: 14 Jul 88 22:54:46 GMT
References: <2743@bath63.ux63.bath.ac.uk> <2148@pt.cs.cmu.edu>
Sender: daemon@bloom-beacon.MIT.EDU
Reply-To: ayermish@athena.mit.edu (Aimee Yermish)
Organization: Massachusetts Institute of Technology
Lines: 29

Actually, it's pretty common for DNA (especially viral DNA) to have
coding sequences which overlap or can be spliced together in different
patterns.  Bear in mind that not every single amino acid in a given
protein is necessary for its folding or its function, and that, in
fact, many proteins have chunks taken out of them after they are
synthesized.  Quite a few organisms use overlapping sequences to
regulate the relative amounts of various proteins.  

As to why, well, if you're a cell, it's a slight advantage to have
less DNA, because it doesn't take so long or so much effort to
replicate.  If you're a virus, you're under a serious constraint: the
size of the capsid that will hold the genome.  There are some really
clever tricks some of those bugs have managed.  One I recall offhand
is a phage that relies on a frameshift error in translation (a rather
uncommon event) to produce very small amounts of lysis protein (what
pops the cell open and lets all the progeny phage free) in
relationship to the amount of coat protein.  In other words, it makes
lots of coat protein (and hence lots of progeny phage) and a very
little lysis protein (a little dab'll do ya, and you don't want to
killl the cell before you're good and ready), all without the messy
waste of regulatory proteins and sequences.  Very elegant...

--Aimee



------------------------------------------------------------------
Aimee Yermish		ayermish@athena.mit.edu
MIT couldn't care less about anything I say. 
(as long as I finish that last paper...)