A research project that used the Genome Sequencer FLX System from 454 Life Sciences has provided an insight into the genomic complexity of the giant mimivirus.
Previous studies have shown that unlike most viruses, the mimivirus has more genes than many bacteria and performs functions that normally occur only in cellular organisms.
The results of the most recent study, published online in the journal Genome Research, suggest that the mimivirus is even more complex than previously thought.
It was led by a team from the Structural and Genomic Information Laboratory at the Mediterranean Institute of Microbiology, in Marseille, France.
Using the Genome Sequencer FLX System from 454 Life Sciences, the researchers performed a viral transcriptome analysis by deep sequencing RNAs expressed by infected amoebas throughout the mimivirus replication cycle.
Unexpectedly, the analysis revealed 75 new genes, including 26 producing non-coding RNAs.
The existence and so far unknown function of these additional genes in the already plethoric mimivirus genome could radically change the current understanding of the way large viruses operate.
Since the discovery and deciphering of its genome in 2004, the giant mimivirus has blurred the traditional boundaries between viruses and cellular organisms, spurring debate between virologists and evolutionary biologists.
'The long reads generated by the GS FLX System were critical for the assembly of full length transcripts, identification of polycistronic mRNA and for the discovery of short transcripts,' said Jean-Michele Claverie and Chantal Abergel, senior authors of the study.
Sequence mapping also allowed the precise delineation of most promoter regions and the identification of the sequence motif governing the early versus late expression of mimivirus genes.
The study also revealed a new promoter element correlating with late gene expression that is also prominent in Sputnik, the recently described mimivirus 'virophage'.
The researchers plan to perform similar viral transcriptome analysis in the presence and absence of various inhibitors and with other amoeba strains that have different sensitivity to the mimivirus.
Since recent metagenomics studies suggest that mimivirus could be the prototype of numerous marine viruses infecting a variety of planktonic micro-organisms, a specific programme will search for the mimivirus's marine relatives in the ongoing international TARA-Oceans expedition.
