The old terms "eclipse phase" or "latent period" describe that part of a virus life cycle when no infectious virus can be extracted from cells which had just been exposed to infectious virions: a good illustration of the concept in terms of a virus assay experiment is shown here.
What happens once a virus is uncoated, or partially uncoated,
depends largely upon what sort of virus it is. The Baltimore Classification of viruses by their genome
types and replication strategies makes it fairly easy to predict the broad sort
of strategy that a virus with a given genome will employ in order to get
replicated. This classification was originally devised by David Baltimore;
it originally only had six categories, but the discovery of "DNA
retroviruses" or PARARETROVIRUSES in the 1980s
has necessitated a new Class VII.
To understand the classification, one must understand how cells replicate their genomes, and express mRNAs, and proteins. This is conveniently explained by the "Watson-Crick Central Dogma", which states that:
INFORMATION FLOW IN CELLS GOES FROM:
DNA TO DNA (REPLICATION)
DNA TO RNA (TRANSCRIPTION)
AND RNA TO PROTEIN (TRANSLATION)
This may conveniently be described in terms of a diagram showing "information flow":
Note: this is an animated GIF file - wait until the whole cycle finishes (+/- 5 sec)
By contrast, viral replication is far more complicated in terms of information flow:
Note: this is an animated GIF file - wait until the whole cycle finishes (+/-20 sec)
The classes are:
| I | dsDNA viruses replicating via DNA (semi-conservative) |
| II | ssDNA viruses replicating via DNA (semi-conservative) |
| III | dsRNA viruses replicating via (+)RNA (conservative?) |
| IV | ssRNA viruses with (+)-sense genomes replicating via RNA (semi-conservative) |
| V | ssRNA viruses with (-)sense
genomes replicating via RNA
(semi-conservative) |
| VI | "diploid"
ssRNA viruses which replicate via reverse transcription with a greater-than-genome-length dsDNA intermediate |
| VII | dsDNA viruses which replicate via reverse transcription with a greater-than-genome-length ssRNA intermediate. |
Copyright Ed Rybicki, August 1997, 1998, March 1999, October
2000, April 2008
(Unless otherwise stated)
