Retroid viruses

[Bruce Phillips]

	A recent review on retroviruses, caulimoviruses, badnaviruses and
retroviruses was published in a recent issue of Adv. Vir. Research.

	The similarities between these viruses include (i) RT activity of
a viral-encoded polymerase, (ii) terminal redundancies in their genomes,
(ii) the genetic map, i.e., gag (capsid)- polymerase- envelope; where
regulatory genes exist, they tend to be positioned after the env gene,
as in the lentiviruses, (iv) the use of dicistronic mRNAs (splicing may
not be common to all these viruses), and (v) the use of trans-activators
or tat factors, although there are some hepadnaviruses, e.g. duck hepatitis
viruses, that do no seem to encode a tat.  On the other hand, the differences
include (i) assembly mechanisms, (ii) requirement to integrate their genome
in order to replicate (only the retroviruses have this obligate requirement), an
and (iii) some are RNA viruses while others are DNA viruses.

	Still, the similarities are striking, more than I appreciated until
I read the aforementioned review.