Biotin protein ligase, C-terminal <p>This C-terminal domain has an SH3-like barrel fold, the function of which is unknown. It is found associated with prokaryotic bifunctional transcriptional repressors [<cite idref="PUB00028009"/>] and eukaryotic enzymes involved in biotin utilization [<cite idref="PUB00028010"/>, <cite idref="PUB00028011"/>]. </p><p> In <taxon tax_id="562">Escherichia coli</taxon> the biotin operon repressor (BirA) is a bifunctional protein. BirA acts both as the acetyl-coA carboxylase biotin holoenzyme synthetase (<db_xref db="EC" dbkey="6.3.4.15"/>) and as the biotin operon repressor. DNA sequence analysis of mutations indicates that the helix-turn-helix DNA binding region is located at the N terminus while mutations affecting enzyme function, although mapping over a large region, are found mainly in the central part of the protein's primary sequence [<cite idref="PUB00028009"/>].</p>