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From: overt@antony (Christian Overton)
Newsgroups: sci.bio
Subject: Re: Sex and organelles (was: chloroplasts)
Message-ID: <16206@burdvax.PRC.Unisys.COM>
Date: 21 Jan 91 21:47:05 GMT
References: <845@frc.frc.maf.govt.nz> <22722@well.sf.ca.us> <1179@ai.cs.utexas.edu>
Sender: news@PRC.Unisys.COM
Reply-To: overt@antony (Christian Overton)
Organization: Unisys - Paoli Research Center   Paoli, PA
Lines: 24
In-reply-to: throop@cs.utexas.edu (David Throop)

In article <1179@ai.cs.utexas.edu>, throop@cs (David Throop) writes:
>    So if sex is so great why don't organelles have it?  Specifically,
>why has there not been evolutionary pressure to move the functions of
>the organelle out of the organelles' DNA onto the chromosomes?  Even
>if the organelles originated from symbiotes, why haven't the two
>genetic legacies been joined over evolutionary time?
>

Actually, most mitochondrial and chloroplast proteins are in fact
coded for by nuclear genes not organelle genes.  A problem with this
arrangement is that proteins synthesized in the cytosol must then be
targeted for the organelle and then transported across the organelle's
membranes.  A signal peptide on the protein directs it to the
organelle where it is then transported across at 'contact sites
(zones)' where the inner and outer membranes join.  Characterization
of the signal peptide and the mechanisms for transport across the
mitochondrial membrane are areas of active research.

Chris
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