Fig. 1.

Schematic representation of various forms of Av1. (A) Av1^wt, the wild-type form that contains a set of P-cluster and FeMoco in each αβ-dimer. (B) Av1^ΔnifH (I), a FeMoco-deficient form that contains a pair of [4Fe–4S]-like clusters in each αβ-dimer. Av1^ΔnifZΔnifB (II), a FeMoco-deficient form that contains a P-cluster in one αβ-dimer and a pair of [4Fe–4S]-like clusters in the other. Av1^ΔnifB (III), a FeMoco-deficient form that contains a P-cluster in each αβ-dimer. Note that the paired [4Fe–4S] clusters in Av1^ΔnifH (I) and Av1^ΔnifZΔnifB (II) presumably represent a precursor form of P-cluster during its assembly process.