Polypeptide composition of higher plant photosystem I complex. Identification of psaI, psaJ and psaK gene products.
High resolution gel electrophoresis of the native photosystem I complex retaining light-harvesting chlorophyll complex revealed the presence of three low-molecular-mass proteins of 7, 4.1 and 3.9 kDa in spinach, and 6.8, 4.4 and 4.1 kDa in pea, in addition to the other well-characterized higher-molecular-mass components. Upon further detergent treatment to deplete light-harvesting chlorophyll complex, the 7 kDa and 4.1 kDa proteins were removed from the photosystem I core complex of spinach, while the 3.9 kDa protein was retained. N-terminal sequencing demonstrated that the 4.1 kDa proteins from both spinach and pea correspond to the gene product of ORF42/44 in chloroplast genome of liverwort and higher plants, which was previously hypothesized as a photosystem I gene (psaJ) based on sequence homology with the cyanobacterial photosystem I component of 4.1 kDa [(1989) FEBS Lett. 253, 257-263]. N-terminal sequence of the spinach 3.9 kDa and pea 4.4 kDa proteins fitted with chloroplast ORF36/40 (psaI) although no homologue has been found in cyanobacteria. The spinach 7 kDa and pea 6.8 kDa proteins correspond to the nuclear-encoded psaK product and significantly matched with the N-terminal sequence of the cyanobacterial 6.5 kDa subunit. The evolutional conservation of the psaJ and psaK seems to suggest their intrinsic role(s) in photosystem I.
Solar Energy Research Group, Institute of Physical and Chemical Research, Saitama, Japan.
M
M
Ikeuchi
A
A
Hirano
T
T
Hiyama
Y
Y
Inoue
D000595:Amino Acid Sequence; D002734:Chlorophyll / Q000302:isolation & purification; D004591:Electrophoresis, Polyacrylamide Gel; D007887:Fabaceae / Q000032:analysis; D045342:Light-Harvesting Protein Complexes; D008969:Molecular Sequence Data; D008970:Molecular Weight; D045322:Photosynthetic Reaction Center Complex Proteins; D045331:Photosystem I Protein Complex; D010940:Plant Proteins / Q000302:isolation & purification; D010944:Plants / Q000032:analysis; D010946:Plants, Medicinal; D012689:Sequence Homology, Nucleic Acid
D045342:Light-Harvesting Protein Complexes; D045322:Photosynthetic Reaction Center Complex Proteins; D045331:Photosystem I Protein Complex; D010940:Plant Proteins; D002734:Chlorophyll