Maintaining organellar genomes - What's the force? (Apr/23/2006 )

Hi,
Anyone knows about the forces that maintain the organeller genomes? Why should the genetic content of the mitochondria and chloroplast not undergo gene transfer to the nuclear genomes?

Plz let me know.

Thanks!

One of the difficult issues is the asymmetry of membrane protein insertion into organelle membranes. Proteins made inside an organelle have membrane localization signals which position them in the correct orientation in the organelle membrane. Moving the protein synthesis to the cytoplasma (and the gene to the nucleus) would require recoding of the targeting signals, and an inversion of the targeting orientation. This would be a difficult process to smoothly navigate with gradual changes.