Reverse transcriptase

[Ed Rybicki]

> From:          "Patrick O'Neil" <patrick at corona>
> Subject:       Re: Reverse transcriptase

> On 24 May 1995, Ed Rybicki wrote:
> > > You are correct, it would be ridiculous for the cell to have reverse 
> > > transcriptase around-
> > 
> > Really?  Funny, that - E coli strains and a number of other related 
> > bacteria (as well as some Archaea) have reverse transcriptases as 
> > part of VERY strange little retrotranspoable elements.  And 
> > retroposons, etc - which are not very retrovirus-like - also have 
> > reverse transcriptases.
> 
> Except that most retroelements ARE very retrovirus-like, some encoding
> gag, pol and other genes in the same order as they are in full
> retroviruses.  The retroelements are considered old, defective viral
> units, in any case.  They would then not be part of the original bacterial
                                                                   ^^^^^^
Don't find retrovirus-like retroelements in bacteria, sorry!  The 
ones you do find are very strange: the nucleic acid you find loose is 
a mixture of ssDNA and RNA, covalently bound back on itself.  The RT 
enzyme and sequence specifiying the NA are also not arranged anything 
like a retrovirus.

> genome, but riders that came along later and now, with the loss of ability
> (or need) to encode capsid and bud (or lyse) the cell, can now be
> considered a permanent fixture within the bacterial genome...hence, they
> have become natural parts of the bacterial genome. 

Would be true if it were like that, but it isn't, so it isn't.  Is 
like that for retrotransposons in Drosophila, yeast, mammals - but 
NOT necessarily for retroPOSONS (NOT the same thing).  A number of 
good reviews out recently, which - not having online ref sources - I 
can't list offhand.  SO: you have elements in eukaryotte genomes 
which transpose via RNA, which do NOT look much like retroviruses, 
and it is debatable whether RVs evolved from them or the othe3r way 
around.  MEANING: that eukaryotic cells do seem to have non-virus 
derived RT around, which seems to have played a role in making (for 
example) intron-less pseudogenes and maybe even some genes...



PS: fix your address "replyto" line!!!
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 |     Ed Rybicki, PhD      |  ed at molbiol.uct.ac.za   |
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