In article <lawrence-270494091539 at ls-12.biology.utah.edu>,
Jeff Lawrence <lawrence at bioscience.utah.edu> wrote:
>> In article <timi-210494183304 at kustu1.berkeley.edu>, timi at mendel.berkeley.edu (Tim Ikeda) writes:
>> > In article <1994Apr21.190914.23337 at dal1>, arlin at ac.dal.ca wrote:
>> >> If these and a few other important characters (circular chromosomes,
>> >> operons, shine-dalgarno sites, etc) were present in the common
>> >> ancestor, as is likely, then archaebacteria and eubacteria have a
>> >> common heritage that I would call "bacterial." [...]
>> >
>>>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
>a slide with numerous linear-chromosome bearing lineages, widespread among
>eubacteria. in each case, however, sister-taxa bore circular chromosomes,
>leading to the conclusion the linearity was a derived character.
>
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
