The DnaJ-Like Zinc-Finger Protein HCF222 Is Required for Thylakoid Membrane Biogenesis in Plants.

To understand the biogenesis of the thylakoid membrane in higher plants and to identify auxiliary proteins required to build up this highly complex membrane system, we have characterized the allelic nuclear mutants () and and isolated the causal gene by map-based cloning. In the ethyl methanesulfonate-induced mutant , the accumulation of the cytochrome (Cytb6f) complex was reduced to 30% compared with the wild type. Other thylakoid membrane complexes accumulated to normal levels.

HCF208, a homolog of Chlamydomonas CCB2, is required for accumulation of native cytochrome b6 in Arabidopsis thaliana.

The cytochrome b(6) subunit of the cytochrome b(6)f complex is a multiheme protein. Two b-type hemes are bound non-covalently to the protein, whereas the third heme (heme c(n)) is covalently attached via an atypical thioether bond. To understand the maturation of cytochrome b(6) and to identify the assisting factors, we characterized the ethyl methanesulfonate-induced nuclear mutant hcf208.

The nuclear-encoded factor HCF173 is involved in the initiation of translation of the psbA mRNA in Arabidopsis thaliana.

To gain insight into the biogenesis of photosystem II (PSII) and to identify auxiliary factors required for this process, we characterized the mutant hcf173 of Arabidopsis thaliana. The mutant shows a high chlorophyll fluorescence phenotype (hcf) and is severely affected in the accumulation of PSII subunits. In vivo labeling experiments revealed a drastically decreased synthesis of the reaction center protein D1.