MreB is a protein found in bacteria that has been identified as a homologue of actin, as indicated by similarities in tertiary structure and conservation of active site peptide sequence.

[1] Indeed, recent studies have found that MreB proteins polymerize to form filaments that are similar to actin microfilaments.

It has been shown to form multilayer sheets comprising diagonally interwoven filaments in the presence of ATP or GTP.

[2] MreB along with MreC and MreD are named after the mre operon (murein formation gene cluster E) to which they all belong.

Members of the Chlamydiota are a notable exception, as these bacteria utilize the protein for localized septal peptidoglycan synthesis.