We have constructed and analysed a cyanobacterial mutant that lacks the put
ative homologue of ycf37, the chloroplast open reading frame 37, which is c
onserved in different algae, but missing in the plastome of higher plants.
In this report we show that Ycf37 of Synechocystis sp. PCC 6803 contains th
ree tetratrico-peptide repeat (TPR) units resembling the structural organiz
ation of Ycf3, a protein that has been suggested to function as a chaperone
during photosystem (PS) I complex formation. We demonstrate a light-activa
ted transcript accumulation of this gent. Inactivation of ycf37 leads to a
lower PSI/PSII ratio and a higher phycocyanin/chlorophyll ratio in Synechoc
ystis cells. The observed alterations in the ycf37 mutants and the structur
al organization of the gene product suggest a functional role in PSI stabil
ity or assembly.