Are introns just junk?

Keith Robison robison1 at
Tue Oct 26 09:02:03 EST 1993

John Logsdon <jlogsdon at> writes:

>Regarding E. coli, I am not quite sure what % of the genome is done
>(Keith Robison are you out there?), but to play the devil's advocate,
>perhaps there is a GrpII in the last gene to be sequenced.  Even if there
>are none in E. coli, it is probably not terribly relevant, since it is
>one of many eubacteria, and not directly on the mt or cp lineage. 
>Regarding selection in E coli vs. Cyanos, perhaps there is less selection
>on genome size in cyanos since I think there are some pretty monstrous
>genomes in cyanos, but the relevance of genome size to introns is unclear
>to me.

You rang, Sir? :-)  E.coli is somewhere between 50% and 60% sequences 
(closer to the 60%).  Other than one truly laughable suggestion (don't
have the reference handy -- available on request next week), there
is no evidence for introns in E.coli.  On the other hand, E.coli 
clearly is under strong streamlining selection (genes are very tightly
packed) and sequencing has been biased towards highly expressed regions.
so we can hold out hope :-)  Of course, treating E.coli as a typical
bacterium is a serious mistake -- not only does it ignore the great
diversity of the bacteria, but E.coli is in some ways "odd" for even
its corner to the tree.  However, sequencing projects from other bacteria
(such as M.leprae and B.subtilis) haven't found any conventional introns either
(though it is quite possible we don't know how to see one).

>birney at writes some more:
>>In eukaryotes that have no introns, is there poly A addition to their

>The blanket answer to these are: I don't know. All are interesting
>though, and perhaps could be answered by looking at some of the
>literature on Giardia molecular biology, since there has been quite a bit
>done on this quite interesting critter.

Probably irrevelant -- polyA addition occurs in E.coli and B.subtilis.

Something I just learned at the meeting I am at which should be of 
interest to a lot of people is that an effort is being made to sequence
the complete genome of Giardia (by Glenn Evans group at the Salk Institute).

Keith Robison
Harvard University
Department of Cellular and Developmental Biology
Department of Genetics / HHMI

robison at 

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