A novel lipothrixvirus, SIFV, of the extremely thermophilic crenarchaeon Sulfolobus

We describe a novel lipothrixvirus, SIFV, of the crenarchaeotal archaeon Su lfolobus islandicus. SIN (S. islandicus filamentous virus) has a linear vir ion with a linear double-stranded DNA genome. These two features coincide i n several crenarchaeotal but not in any other viruses. The SIFV core is for med by a zipper-like array of DNA-associated protein subunits and is covere d by a lipid envelope containing host lipids. We sequenced similar to 96% o f the virus genome excepting the DNA termini, which were modified in an unu sual, yet uncharacterized, manner. Both, the 5' and the 3' DNA termini were insensitive to enzymatic degradation and labelling. Two open reading frame s (ORFs) of the SIFV genome are likely to encode helicases and resemble unc haracterized ORFs from other archaea in sequence. Three ORFs showed sequenc e similarity with each other and each contained a glycosyl transferase moti f. Another ORF of the SIFV genome showed significant sequence similarity to the ORF a291 from the well characterized, spindle-shaped Sulfolobus virus SSV1. Due to its structure, SIFV is classified as a lipothrixvirus. (C) 200 0 Academic Press.