Figure 4.

The iscS mutant has reduced FNR activity that can be complemented by the addition of iscS in trans. FNR activity was measured by assaying the amount of β-galactosidase (Miller units) produced in strains grown under anaerobic conditions containing the FNR-dependent dmsA′∷lacZ promoter fusion. The genotypes are indicated below the figure. Complemented strains contained either pPK4196 (iscS) or pPK4194 (iscSUA) and as with complemented strains in Figs. 2 and 3, expression of the isc gene(s) depended on fortuitous promoter elements from the vector (pET11a). The strains are all derivatives of either PK3292 (FNR⁺) or PK3293 (FNR^-; Table 1).