More is not always better. Viruses know this best, as many of the species of viruses have evolved to have a genome reduced to beyond minimalistic. They have kept the ultimate minimum of protein-encoding genes, often hijacking the host cell DNA and protein synthesizing machinery to replicate.
ssDNA and RNA are not for storing
In cellular organisms the occurrence of a single stranded DNA (ssDNA) is considered genetic damage and complex machinery is employed to repair it even in the most simple bacteria. RNA is usually only used to process genetic information, but not for storing it. Viruses are bold and creative – some viruses are not only skilled in compressed coding, but are even more creative in coding their genes in ssDNAs or RNAs. Such boldness is never tolerated in cellular organisms and may be that is why viruses end up to being the ultra-successful pragmatics of nature.
The tiny virus
The Procine circovirus type 1 (PCV1) is the smallest virus know yet. Its genome contains only 1759 nucleotides, organized in a ssDNA, covalently closed in a circular form. As a comparison – there are at least 10 known genes longer than the whole genome of PCV1! In all fairness, the genome of PCV1 actually contains three genes – one for the capsid protein (the protein surrounding the ssDNA), and two for replicase proteins (used in the viral multiplication in the cell). For being so small and simple PCV1 and its cousin (PCV2) can cause some nasty diseases in animals and humans alike.
Little but lethal
The ingenuity of those viruses does not stop at surviving with a ssDNA. They succeeded to squeeze in the code of another gene (which has been shown to not be essential for the viral life cycle), which is able to modulate the host-cell cycle and induce a viral induced apoptosis. This one single gene is able to interact with a E3-ligase – one of the major proteins in the cellular recycling pathways (the ubiquitin pathway). By being in the way of the interaction between E3-ligase and its subsequent transcription factors brings a halt to the cell cycle and the activation of the cell-death pathway. When that happens to a cell full of newly replicated PCV1 particles, they get released into the tissue and are able to infect new cells.
This article was written with more characters than the total ATGCs used to compose the whole PCV1 genome! 🙂
(title picture from here)