Targeted inactivation of the smallest plastid genome-encoded open reading frame reveals a novel and essential subunit of the cytochrome b(6)f complex. |
| |
Authors: | M Hager K Biehler J Illerhaus S Ruf and R Bock |
| |
Institution: | Institut für Biologie III, Universität Freiburg, Schänzlestrasse 1, D-79104 Freiburg, Germany. |
| |
Abstract: | The smallest conserved open reading frame in the plastid genome, ycf6, potentially specifies a hydrophobic polypeptide of only 29 amino acids. In order to determine the function of this reading frame we have constructed a knockout allele for ycf6. This allele was introduced into the tobacco plastid genome by chloroplast transformation to replace the wild-type ycf6 allele. Homoplasmic Deltaycf6 plants display a photosynthetically incompetent phenotype. Whereas the two photosystems are intact and physiologically active, we found that the electron transfer from photosystem II to photosystem I is interrupted in Deltaycf6 plants. Molecular analyses revealed that this block is caused by the complete absence of the cytochrome b(6)f complex, the redox-coupling complex that interconnects the two photosystems. Analysis of purified cytochrome b(6)f complex by mass spectroscopy revealed the presence of a protein that has exactly the molecular mass calculated for the Ycf6 protein. This suggests that Ycf6 is a genuine subunit of the cytochrome b(6)f complex, which plays a crucial role in complex assembly and/or stability. We therefore propose to rename the ycf6 reading frame petN. |
| |
Keywords: | |
|
|