Studies on transcription controls operating in archaeal virus-host systems: regulation of transcription of genomes of the rudiviruses SIRV1 and SIRV2, and the lipothrixvirus SIFV of the hyperthermophilic archaeaon Sulfolobus

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A pair of rod-shaped viruses SIRV1 and SIRV2 of hyperthermophilic Sulfolobus, the genomes of which have been recently completely sequenced, is an attractive and unique model for unravelling mechanisms, controls and signal structures involved in gene expression in Archaea. The virus SIRV1 responds to changes of a host in a way unusual for DNA viruses by extensive and rapid accumulation of point mutations in the genome. This allows rapid selection of new virus variants adapted to a new host, coinciding with a recovery of high fidelity of replication. In contrast to the genome of SIRV1, the genome of SIRV2, which is highly homologous to the latter, however, 3.2 kb longer, remains unchanged in the same hosts. In order to understand the SIRV1-specific mutator system and its control we plan to study transcription and replication of the genomes of the two viruses. Comparative studies of transcripts of the genomes of SIRV1 and SIRV2 in different hosts will enable us to identify candidate genes that are involved in a response to changes of host species, and those which cause differences in the behaviour of the viruses under such conditions. These genes will be selectively disrupted, or deleted/introduced from/into the DNAs of the viruses by constructing recombinant DNA molecules consisting of different portions of the genomes of the two viruses in a way not affecting essential viral functions. Transfection of an appropriate host with these DNAs and studies on their replication and transcription will shed light on functions of proteins encoded by the genes and controls of their expression. The studies will also enable to identify ORFs which are nonessential for virus function, and lay the basis for the development of a transformation vector based on the virus DNAs.