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." [...]
>> Just an aside...
> It's time to throw out the "bacteria only have circular chromosomes" idea.
>> See: Davidson BE; MacDougall J; Saint Girons I. 1992.
> Physical map of the linear chromosome of the bacterium Borrelia
> burgdorferi 212, a causative agent of Lyme disease, and localization
> of rRNA genes. J. Bacteriol.174:3766-74.
>> The cool question is: What system/s does a bacterium use to maintain a
> linear chromosome?
>> - Tim Ikeda (timi at mendel.berkeley.edu)
Certainly its a cool question, but saying (as I did) that bacteria
*ancestrally* have circular chromosomes is not the same as saying
"bacteria only have circular chromosomes" (Tim's words, not mine).
Linear bacterial chromosomes are, as far as I know, restricted to
members of the spirochete genus _Borrelia_, and the inference that
circular chromosomes are ancestral is therefore a sound one.