This family represents the N-terminal region of the bacterial poly-beta-hydroxybutyrate polymerase (PhaC). Polyhydroxyalkanoic acids (PHAs) are carbon and energy reserve polymers produced in some bacteria when carbon sources are plentiful and another nutrient, such as nitrogen, phosphate, oxygen, or sulfur, becomes limiting. PHAs composed of monomeric units ranging from 3 to 14 carbons exist in nature. When the carbon source is exhausted, PHA is utilized by the bacterium. PhaC links D-(-)-3-hydroxybutyrl-CoA to an existing PHA molecule by the formation of an ester bond. This family appears to be a partial segment of an alpha/beta hydrolase domain.