HF2 is a haloarchaeal virus infecting two Halorubrum species (Family 
Halobacteriaceae). It is lytic, has a head-and-tail morphology and belongs to 
the Myoviridae (contractile tails). The linear double-stranded DNA genome was 
sequenced and found to be 77 670 bp in length, with a mol% G+C of 55.8. A total 
of 121 likely open reading frames (ORFs) were identified, of which 37 overlapped 
at start and stop codons. The predicted proteins were usually acidic (average pI 
of 4.8), and less than about 12% of them had homologues in the sequence 
databases. Four complete tRNA-like sequences (tRNA-Arg, -Asx, -Pro and -Tyr) and 
an incomplete tRNA-Thr were detected. A transcription map showed that most of 
the genome was transcribed and that the synthesis of transcripts occurred in a 
highly organized and reproducible pattern over a 5 h infection cycle. 
Transcripts often spanned multiple ORFs, suggesting that viral genes were 
organized into operons. The predicted ORF and observed transcript directions 
matched well and showed that transcription is mainly directed inwards from the 
genome termini, meeting at about 45-48 kb, and this was also a turning point in 
a cumulative GC-skew plot. The low point in cumulative GC-skew, near the left 
end, was a region rich in short repeats and lacking ORFs, which is likely to be 
an origin of replication. The HF2 genome is a mosaic of components from widely 
different sources, demonstrating clearly that viruses of haloarchaea, like their 
bacteriophage counterparts, are vectors for the exchange and transmission of 
genetic material between wide taxonomic distances, even across domains.