This is a lesson on the evolution of the E. coli chromosome a la Karl Lark, Prof emeritus, Univ of Utah, and Millie Masters, Senior Lecturer, Univ. of Edinburgh

Today the map of E.coli looks like this. "oriC" is the origin of Chromosome replication. The other sites are for malic dehydrogenase (Krebs Cycle), lactic dehydrogenase (glycolysis), and isocitric dehydrogenase (Krebs Cycle). The "?" is of unknown function - if it exists at all.

The Lark/Masters hypothesis of the formation of this goes as follows. At the dawn of the enteric bacteria was one that had a small genome that had enzymatic activities that were not quite so refined as they are today. Of course it had to have an oriC, and among the other genes was we might call the initial dehydrogenase, "idh". It would transfer electrons to any alpha-keto-compound. A very generalized, non-specific enzyme in this eoenteric ("dawn" enteric).

Somehow, when by chance an eoenteric was dividing it made a mistake and the two daughter chromosomes tandemized into a larger circle. Now there were two identical copies of idh in mirror image places on the genome.

These two identical genes then were free to undergo divergent evolution. The most proficient cell was one that diverged such that the two enzymes became more specialized and faster.

Then, guess what! One of the late meso-enterics made a mistake and tandemized its genome to form one that was four-times the size of the eo-enteric. Now you see the potential for four different divergences of the original idh.

The question is: while three of these genes (LDH, MDH and iCDH) do exist. How much homology really exists that would support the Lark/Masters model? And can anything be found at the corresponding "?" point?

These will be studies appropriate to the GenBank website.

Now throw in moveable elements and transposons!

I want to go to the TOP OF PAGE or ESCAPE!