Characterization of a Synechocystis double mutant lacking the photosystem II assembly factors YCF48 and Sll0933.

The de novo assembly of photosystem II (PSII) depends on a variety of assisting factors. We have previously shown that two of them, namely, YCF48 and Sll0933, mutually interact and form a complex (Rengstl et al. in J Biol Chem 286:21944-21951, 2011). To gain further insights into the importance of the YCF48/Sll0933 interaction, an ycf48 ( - ) sll0933 ( - ) double mutant was constructed and its phenotype was compared with the single mutants' phenotypes. Analysis of fluorescence spectra and oxygen evolution revealed high-light sensitivity not only for YCF48 deficient strains but also for sll0933 ( - ), which, in addition, showed reduced synthesis and accumulation of newly synthesized CP43 and CP47 proteins in pulse-labeling experiments. In general, the phenotypic characteristics of ycf48 ( - ) sll0933 ( - ) were dominated by the effect of the ycf48 deletion and additional inactivation of the sll0933 gene showed only negligible additional impairments with regard to growth, absorption spectra and accumulation of PSII-related proteins and assembly complexes. In yeast split-ubiquitin analyses, the interaction between YCF48 and Sll0933 was confirmed and, furthermore, support for direct binding of Sll0933 to CP43 and CP47 was obtained. Our data provide important new information which further refines our knowledge about the PSII assembly process and role of accessory protein factors within it.