Genetic requirements for the function of the archaeal virus SSV1 in Sulfolobus solfataricus: construction and testing of viral shuttle vectors.
Directed open reading frame (ORF) disruption and a serial selection technique in Escherichia coli and the extremely thermophilic archaeon Sulfolobus solfataricus allowed the identification of otherwise cryptic crucial and noncrucial viral open reading frames in the genome of the archaeal virus SSV1. It showed that the 15. 5-kbp viral genome can incorporate a 2.96-kbp insertion without loss of viral function and package this DNA properly into infectious virus particles. The selection technique, based on the preferential binding of ethidium bromide to relaxed DNA and the resulting inhibition of endonuclease cleavage to generate a pool of mostly singly cut molecules, should be generally applicable. A fully functional viral shuttle vector for S. solfataricus and E. coli was made. This vector spreads efficiently through infected cultures of S. solfataricus, its replication is induced by UV irradiation, it forms infectious virus particles, and it is stable at high copy number in both S. solfataricus and E. coli. The classification of otherwise unidentifiable ORFs in SSV1 facilitates genetic analysis of this virus, and the shuttle vector should be useful for the development of genetic systems for Crenarchaeota.