β-galactosidase activity of E. coli strain ET8000 carrying phbF::lacZ or phbP1::lacZ fusion (plasmids pKADO5 and pMMS35, respectively). Assays were performed as described in Material and Methods. The His-PhbF protein was expressed by the tac promoter from the plasmid pMMS31. Data represents the average ± standard deviation of at least three independent determinations. Background activity of cells carrying pMP220 (control vector) in the presence of pMMS31 was less than 6 Miller units.