Is the F plasmid a viroid?

Gene Cutler genecutl at mendel.Berkeley.EDU
Thu Dec 2 18:42:53 EST 1993

In article <plyjmh.2.0010ECB3 at> you write:
>The F plasmid seems to behave similarly to a viroid.  It causes its host
>to replicate and spread it to a new host.
>Is this a good analogy?
>Mazda Hewitt

F plasmids, like bacteriophages, can be considered as parasitic DNAs.
In the case of phages, the DNA codes for a protein coat which lets the
virus travel from one host to another on its own, while in the case of
F plasmids, the DNA codes for genes which cause their hosts to directly
conjugate with an F- cell.

This is why people have proposed the model that sex originated because
of parasitic DNA's attempts to spread around (pardon the anthropomorphism)
and happened to also benefit the host. In the case of F plasmids I doubt
that the host is benefited unless the F plamsid is actually an F' and carried
something like antibiotic resistance.  This is something that actually

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