ASCE (the additional strand catalytic E division) is one of the major division of P-loop NTPases.Bioinformatic analysis showed that a group of the ASCE proteins contains an additional PIN domain (Pili N-terminal domain) at the N-terminal and is highly conserved and specific in archaea.We found that the gene in Sulfolobobus islandicus Rey15A could not be knocked out and was likely essential for cell viability.The protein is a divalent cation-dependent ATPase and therefore we designed it as PINA (for PIN-domain ATPase).