PhoA-LacZ enzymes activities and strength indexes of cells carrying the pHKU1601 plasmid series. (a) Relative PhoA and LacZ (β-gal) activities are presented as means ± standard error, which were obtained by linear regression through at least 20 data points obtained from 5 replicates. To normalize PhoA activities, the maximum PhoA activity recorded in the experiment (pHKU1601-337) was transformed to 1 and PhoA activities of other samples were expressed as a percentage relative to this maximum value. The same procedure was applied to normalize LacZ activities using the activity from pHKU1601-532 as the maximum. The end points of Deh4p in the recombinants are indicated. When a number is shifted downward it implies that the reporter was located in the periplasm. (b) A bar-chart showing the strength indexes of the recombinants shown in (a). When a normalized activity value was zero an arbitrary small value, 0.0001, was assigned to prevent logging a zero or undefined number in calculating the strength index. A positive value for the strength index indicates that the reporter ended in the periplasm and a negative value suggests that the reporter ended in the cytoplasm. The strength index was defined as Ln(normalized PhoA activity/normalized LacZ activity).