<p> The member of this family from <taxon tax_id="1063">Rhodobacter sphaeroides</taxon> (Rhodopseudomonas sphaeroides) has been shown both to form a complex with sigma(E) and to negatively regulate tetrapyrrole biosynthesis. This protein likely contains (at least) two distinct functional domains as several smaller homologues (excluded in this entry) show homology only to the C-terminal region including a motif: PxHxHxGxE.</p>