Huzuru Husimi
Department of Functional Materials Science,
Saitama University,
Urawa 338-8570, Japan
Non-enveloped viruses such as simple bacteriophages
have a unique strategy of linking of a genotype
to phenotype. The molecule of genotype is
bound to some molecules of the phenotype.
In short, genomic DNA/RNA is bound to coat
proteins. On the other hand, cellular organisms
adopt another kind of the strategy, namely
the compartmentalizing of both genotype and
phenotype molecules with a cell membrane.
Development of evolutionary molecular engineering
has demonstrated that the virus-type strategy
is very efficient for the evolution of single
protein. Examples are cellstat, phage-display,
ribosome-display, and ``in vitro virus''
( or mRNA/DNA protein fusion) methods. Its
efficiency must correspond to the faster
evolution of a virus in nature than cellular
organism. Many authors believe the viruses
emerged after the evolution of cellular organism,
because viruses are cell parasites. The ``in
vitro virus'', however, can reproduce without
a cell. The definition of a virus and a cell
based on the strategy to link genotype to
phenotype, we proposed a virus-early/cell-late
model of the history of life.
The first encoded protein was assumed to
be a cofactor of replication ribozyme in
the RNA world and to be bound to its genetic
RNA. As such a virus-type strategy could
introduce the Darwinian selection process
into the hypercycle with translation, a hypercycle
with virus-like members could make both the
first encoded protein (replicase) and the
translation machinery
evolve gradually out of the RNA world without
a proto-cell, even if the parasitically emerging
translation reaction was a serious genetic
load in the initial phase. Moreover, it was
shown they could evolve much faster by this
virus-type strategy than by a primitive cellular
organism.
References: N.Nemoto and Y,Husimi, J.Theor.Biol.
(1995) 176, 67-77; N.Nemoto et al, FEBS Lett.(1997)
414A405-408