<p>In eukaryotes, there are three different forms of DNA-dependent RNA polymerases (<db_xref db="EC" dbkey="2.7.7.6"/>) transcribing different sets of genes. Each class of RNA polymerase is an assemblage of ten to twelve different polypeptides. In archaebacteria, there is generally a single form of RNA polymerase which also consists of an oligomeric assemblage of 10 to 13 polypeptides.Archaebacterial subunit N (gene rpoN) [<cite idref="PUB00004866"/>] is a small protein of about 8 kDa, itis evolutionary related [<cite idref="PUB00002250"/>] to a 8.3 kDa component shared by all three forms ofeukaryotic RNA polymerases (gene RPB10 in yeast and POLR2J in mammals) as wellas to <taxon tax_id="10497">African swine fever virus</taxon> (ASFV) protein CP80R [<cite idref="PUB00015097"/>].</p><p>This signature spans the conserved region, which is located at theN-terminal extremity of these polymerase subunits; this region contains twocysteines that binds a zinc ion [<cite idref="PUB00015096"/>].</p>