Targeted deletion of psaJ from the cyanobacterium Synechocystis sp. PCC 6803 indicates structural interactions between the PsaJ and PsaF subunits of photosystem I.
Photosystem I catalyzes the light-driven oxidation of plastocyanin or cytochrome c6 and the reduction of ferredoxin or flavodoxin. PsaJ is a 4.4 kDa hydrophobic subunit of photosystem I from cyanobacteria and chloroplasts. To investigate the function of PsaJ, we generated a mutant strain of the cyanobacterium Synechocystis sp. PCC 6803 in which the psaJ gene is replaced by a gene for chloramphenicol resistance. Deletion of psaJ led to a reduction in the steady state RNA level from psaF which is located upstream from psaJ. Immunoquantification using an anti-PsaF antibody revealed a significant decrease in the amount of PsaF in membranes of the mutant strain. Trimeric photosystem I complexes isolated from the mutant strain using n-dodecyl beta-D-maltoside lacked PsaJ, contained ca. 80% less PsaF, but maintained wild-type levels of other photosystem I subunits. In contrast, the photosystem I purified using Triton X-100 contained less than 2% PsaF when compared to the wild type, showing the more extractable nature of PsaF in PsaJ-less photosystem I in the presence of Triton X-100. PsaE was more accessible to removal by NaI in a mutant strain lacking PsaF and PsaJ than in the wild type. The presence of PsaF in photosystem I from the PsaJ-less strain did not alter the increased susceptibility of PsaE to removal by NaI. These results indicate an interaction between PsaJ and PsaF in the organization of the complex.
Xu
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Division of Biology, Kansas State University, Manhattan 66506-4901.
Odom
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Guikema
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Chitnis
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Chitnis
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D001426:Bacterial Proteins; D002462:Cell Membrane / Q000737:chemistry; D000458:Cyanobacteria / Q000235:genetics / Q000378:metabolism*; D003902:Detergents; D018390:Gene Targeting; D005960:Glucosides; D008565:Membrane Proteins; D008970:Molecular Weight; D017830:Octoxynol; D045322:Photosynthetic Reaction Center Complex Proteins / Q000032:analysis / Q000737:chemistry* / Q000235:genetics; D045331:Photosystem I Protein Complex; D011487:Protein Conformation; D012329:RNA, Bacterial / Q000032:analysis; D012333:RNA, Messenger / Q000032:analysis; D017384:Sequence Deletion / Q000502:physiology*; D012974:Sodium Iodide
D001426:Bacterial Proteins; D003902:Detergents; D005960:Glucosides; D008565:Membrane Proteins; D045322:Photosynthetic Reaction Center Complex Proteins; D045331:Photosystem I Protein Complex; D012329:RNA, Bacterial; D012333:RNA, Messenger; C085831:photosystem I, PsaJ subunit; C079742:psaF protein, bacteria; C040358:dodecyl maltoside; D017830:Octoxynol; D012974:Sodium Iodide