This model describes a family of small proteins found associated with inclusions in bacterial cells. Most associate with polyhydroxyalkanoate (PHA) inclusions, the most common of which consist of polyhydroxybutyrate (PHB). These are designated granule-associate proteins or phasins; the member from Rhodospirillum rubrum is an activator of polyhydroxybutyrate (PHB) degradation. However, the member from Magnetospirillum sp. AMB-1 is called a magnetic particle membrane-specific GTPase.