Present in all three domains of cellular life. Four copies in the transcriptional coactivator p100: these, however, appear to lack the active site residues of Staphylococcal nuclease. Positions 14 (Asp-21), 34 (Arg-35), 39 (Asp-40), 42 (Glu-43) and 110 (Arg-87) [SNase numbering in parentheses] are thought to be involved in substrate-binding and catalysis.
Staphylococcus aureus nuclease (SNase) homologues, previously thought to be restricted to bacteria and archaea, are also in eukaryotes. Staphylococcal nuclease has a multi-domain organisation [PUBMED:9003410]. The human cellular coactivator p100 contains four repeats, each of which is a SNase homologue. These repeats are unlikely to possess SNase-like activities as each lacks equivalent SNase catalytic residues, yet they may mediate p100's single-stranded DNA-binding function [PUBMED:9041650]. A variety of proteins including many that are still uncharacterised belong to this group.
Callebaut I, Mornon JP; , Biochem J 1997;321:125-132.: The human EBNA-2 coactivator p100: multidomain organization and relationship to the staphylococcal nuclease fold and to the tudor protein involved in Drosophila melanogaster development. PUBMED:9003410 EPMC:9003410.