The archetype is archaeal protein SSO1653 which is the sole Snf2 family member in Sulfolobus solfataricus. It is encoded in the P2 strain genome by juxtaposing SSO1653 and SSO1655 genes, punctuated by transposase SSO1654 inserted into the second recA domain immediately upstream of motif V. Whilst it is highly unlikely that a Snf2 family enzyme would be functional with an atypical 40kD insertion at this conserved part of the protein, the enzyme with transposase removed has biochemical activity and was used successfully for structure determination 1. The transposase appears to be active, such that a full length gene can be cloned with appropriate screening (MF White, personal communication). We subsequently refer to this protein without the transposase as SSO1653.

No information is available for the biological role of any member, but biochemical analysis associated with the structure determination showed that this protein can generate DNA torsion in an ATP-dependent manner analogous to eukaryotic Snf2 family proteins 1.

The SSO1653 subfamily helicase-like region also shows close linkage with a zinc finger SWIM motif that may bind to nucleic acids 2, 3. For example, immediately downstream of the S solfataricus SSO1653-1655 gene is a coordinately regulated gene SSO1656 encoding a 26kdal basic protein containing the SWIM motif. An SSO1653 subfamily member is present in all Bacillus and Streptococcus genomes 4, and many of these polypeptides also carry a SWIM motif in the same polypeptide. Those polypeptides with a Snf2 family helicase-like region but lacking a SWIM motif appear to be in the same operon as a second smaller protein which carries the SWIM motif instead 3. Although the SWIM motif also occurs in eukaryotes, it has not been linked to any of the eukaryotic Snf2 family proteins 3.