This family consists of bacterial MreB and Mbl proteins as well as two related archaeal sequences. MreB is known to be a rod shape-determining protein in bacteria and goes to make up the bacterial cytoskeleton. Genes coding for MreB/Mbl are only found in elongated bacteria, not in coccoid forms. It has been speculated that constituents of the eukaryotic cytoskeleton (tubulin, actin) may have evolved from prokaryotic precursor proteins closely related to today's bacterial proteins FtsZ and MreB/Mbl [1].

1: Cytoskeletons in prokaryotes. Mayer F; Cell Biol Int 2003;27:429-438. PMID:12758091