<p>This entry represents a structural motif found in demethylmenaquinone methyltransferases and in the regulator of ribonuclease E activity A (RraA). These proteins contain a swivelling 3-layer beta/beta/alpha domain that appears to be mobile in most multi-domain proteins known to contain it. These proteins are structurally similar, and may have distant homology, to the phosphohistidine domain of pyruvate phosphate dikinase. The RraA fold is an ancient platform that has been adapted for a wide range of functions. RraA had been identified as a putative demethylmenaquinone methyltransferase and was annotated as MenG, but further analysis showed that RraA lacked the structural motifs usually required for methylases. </p><p>The <taxon tax_id="562">Escherichia coli</taxon> protein regulator RraA acts as a trans-acting modulator of RNA turnover, binding essential endonuclease RNase E and inhibiting RNA processing [<cite idref="PUB00017730"/>]. RNase E forms the core of a large RNA-catalysis machine termed the degradosomes. RraA (and RraB) causes remodelling of degradosome composition, which is associated with alterations in RNA decay and global transcript abundance and as such is a bacterial mechanism for the regulation of RNA cleavage.</p><p>Demethylmenaquinone methyltransferases convert dimethylmenaquinone (DMK) to menaquinone (MK) in the final step of menaquinone biosynthesis. </p><p>This region is also found at the C terminus of the DlpA protein <db_xref db="SWISSPROT" dbkey="Q48806"/>.</p>