In article <Coxq39.1CG at gpu.utcc.utoronto.ca>, lamoran at gpu.utcc.utoronto.ca (L.A. Moran) writes:
> In article <lawrence-270494091539 at ls-12.biology.utah.edu>,
> Jeff Lawrence <lawrence at bioscience.utah.edu> wrote:
>>>>While i agree that circular chromosomes are likely to be ancestral to the
>>bacterial lineage, linear chromosomes and linear plasmids are widespread
>>among bacterial taxa. Aside from Borrelia (Casjens Mol Micro, May 93), i
>>can recall that Agrobacterium (J Bact, Dec 93) and Streptomyces (MGG, Nov
>>93) also have linear chromosomes. I also recal sherwood casjens popping up
Thanks for this list of my earlier oversights.
> The common ancestor of all bacteria may have had circular chromromsome(s) but
> whether the common ancestor of all life had linear or circular chromosome(s)
> is an open question. (Assuming that the root of the universal tree falls
> between prokaryotes and eukaryotes.) Circular chromosomes may still be a
> derived character in prokaryotes.
>> Larry Moran
>Agreed. I'm not making alot of assumptions about the universal tree. The
Iwabe-Gogarten tree, the Eocyte/Woese&Wolfe tree, the Gupta tree--
all of these trees have organisms with bacterial features (circular
chromosomes, operons, etc) on *both* sides of the root, and
thus if any of these trees are correct, the most recent common
ancestor of all cells was likely to have been a bacterium
_sensu latu_. If Larry's suggestion that euks may be an outgroup
to bacteria _sensu latu_ is correct, then, as Larry suggests,
circular chromosomes and other characteristic bacterial features
may be derived states rather than primitive ones.
Arlin
