Cells of S.solfataricus, strain P2, were grown in minimal salts culture media supplemented with yeast extract (0.1%), casamino acids (0.1%), plus glucose (0.1%) (YGM) or sucrose (0.1%) (YSM). The extraction of total RNA was performed as reported previously (24) . Total RNA was extensively digested with DNAse (Ambion, Austin, TX, USA) and the absence of DNA was assessed by the lack of PCR amplification with each sets of primers described below. The RT-PCR experiments were performed as reported previously (24) by using the primers described previously that allowed the amplification of a region of 833 nt (positions 1-833, in which the A of the first ATG codon is numbered as one) overlapping the ORFs SSO11867 and SSO3060 (24) .