<taxon tax_id="4932">Saccharomyces cerevisiae</taxon> strains containing the erg8-1 mutation are temperature sensitive for growth due to a defect in phosphomevalonate kinase, an enzyme of isoprene and ergosterol biosynthesis. Subcloning and DNA sequencing have defined the functional ERG8 regulon as an 850bp upstream region and an adjacent 1,272bp open reading frame. The deduced ERG8 protein contains 424 residues and shows no similarity to known proteins, except within a putative ATP-binding domain present in many kinases [<cite idref="PUB00003676"/>]. Enzymes that share the N-terminal Gly/Ser-rich putative ATP-binding region include galactokinase, homoserine kinase, mevalonate kinase and phosphomevalonate kinase. Homoserine kinase is a homodimeric enzyme involved in threonine biosynthesis. Sequence comparison of the yeast enzyme with the corresponding proteins from bacterial sources reveals the presence of several highly conserved regions, the pattern of occurrence of which suggests that the ancestral sequences might have been composed from separate (functional) domains. A block of similar residues, found towards the C terminus,is also present in many other proteins involved in threonine (or serine) metabolism; this motif may therefore represent the binding site for the hydroxy-amino acids. Limited similarity was detected between a motif conserved among the homoserine kinases and consensus sequences found in other mono- or dinucleotide-binding proteins [<cite idref="PUB00001384"/>].