A Virus: mediator of encoded protein evolution

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