<p>This entry represents domains with a ribbon-helix-helix core topology consisting of four helices in an open array of two hairpins. Such domains are found in several bacterial and phage repressors, including the <taxon tax_id="562">Escherichia coli</taxon> methionine repressor (MetJ), which when combined with S-adenosylmethionine (SAM) represses the expression of the methionine regulon and of enzymes involved in SAM synthesis [<cite idref="PUB00013999"/>]. Other bacterial and phage repressors containing domains with a similar fold include the bacterial plasmid-encoded repressors CopG (<db_xref db="INTERPRO" dbkey="IPR002145"/>), the bacterial omega transcription repressor [<cite idref="PUB00014024"/>], and the phage repressors Arc [<cite idref="PUB00014000"/>] and Mnt [<cite idref="PUB00014001"/>]. These repressors are usually obligate dimers, which pair through a single N-terminal strand, and possess a C-terminal helix-turn-helix unit [<cite idref="PUB00016689"/>].</p>