FIG. 1.

A model is presented for the classes of proposed pseudorevertant mutations that could allow stable assembly and photosynthetic activity of PS I. Class I, suppressor mutations lessening the flow of electrons to PS I, limiting reduction of the quinone pool and photooxidative damage to PS I; class II, intergenic mutations in a reaction center subunit, PsaB, allowing for assembly of a genetically altered PsaC subunit; class III, an extragenic suppressor that is not within PS I but influences its expression, stability, or activity.