CLONING AND SEQUENCING OF THE GENE CODING FOR S-ADENOSYLHOMOCYSTEINE HYDROLASE IN THE THERMOPHILIC ARCHAEON SULFOLOBUS-SOLFATARICUS

The gene from the thermophilic archaeon Sulfolobus solfataricus (Ss), encoding the S-adenosylhomocysteine hydrolase (AdoHcyHD), has been clo ned. Two degenerate oligodeoxyribonucleotide (oligo) probes, synthesiz ed on the basis of amino acid (aa) sequence of cyanogen bromide-peptid e fragments of the purified protein, were used to screen a genomic lib rary of Ss cloned into the pGEM7Zf(+) vector. The AdoHcyHD gene (adohc yhd) comprises 1254 nucleotides (nt) and encodes a polypeptide of 417 aa with a deduced molecular mass of 46 kDa, in good agreement with the value directly measured for the purified enzyme. The identity of more than 32% of the deduced aa sequence was confirmed by Edman degradatio n of peptides. Putative regulatory elements which are in good agreemen t with the archaeal promoter consensus sequences were identified in th e flanking regions. Comparison of the aa sequences of AdoHcyHD from di fferent sources shows a remarkable degree of conservation. Surprisingl y, several aa residues, thought important in substrate binding and cat alysis, show non-conserved replacements in Ss AdoHcyHD.