<p>This domain appears to be ubiquitous in bacteria and is often linked to a regulatory domain, such as a phosphorylation receiver or oxygen sensing domain. Its function is to synthesize cyclic di-GMP, which is used as an intracellular signalling molecule in a wide variety of bacteria [<cite idref="PUB00016966"/>,<cite idref="PUB00016967"/>]. Enzymatic activity can be strongly influenced by the adjacent domains. Processes regulated by this domain include exopolysaccharide synthesis, biofilm formation, motility and cell differentiation.</p> <p>Structural studies of PleD from <taxon tax_id="155892">Caulobacter crescentus</taxon> show that this domain forms a five-stranded beta sheet surrounded by helices, similar to the catalytic core of adenylate cyclase [<cite idref="PUB00016971"/>].</p>