Updated project metadata. An increasing number of small proteins has been identified in the genomes of well-annotated model organisms including photosynthetic cyanobacteria such as Synechocystis sp. PCC 6803. A newly assigned protein comprising 37 amino acids was analyzed that is encoded upstream of the super-oxide dismutase SodB encoding gene. The initial hypothesis that this small protein might be functionally related to SodB could not be supported, instead we provide evidence that it fulfills important functions related to the organization of photosynthetic complexes. Therefore, we named it small light-induced protein of 4 kDa, SliP4. SliP4 is strongly induced under high-light-conditions and it is co-localized to photosystem I and II as well as NDH1 complexes on thylakoid membranes. Tagged SliP4 was used to purify NDH1 complexes, where it is especially associated with the subunits NdhF1 and NdhD1. Mutation of the protein-coding part in the sliP4 gene resulted in a high-light-sensitive phenotype, because the mutant was not further able to induce cyclic electron flow and state transitions under high-light conditions. Collectively our data indicate that SliP4 contributes to the association of NDH1 with the photosystem I and/or photosystem II complexes to facilitate different electron transfer modes under high light conditions.