Analysis of SyR1 - a sRNA regulating photosynthesis in Synechocystis sp. PCC6803

Post-transcriptional gene regulation by trans encoded small RNAs (sRNA) emerges as a regulatory feature common to most prokaryotes. Recently, biocomputational prediction [1], comparative transcriptional analysis [2] and high throughput pyrosequencing of Synechocystis sp. PCC6803 [3] revealed the existence of many new sRNAs in this cyanobacterial model organism. One of these candidates is the strongly accumulating sRNA SyR1 (Synechocystis ncRNA 1), which is a 130 nt long transcript from the intergenic region between the fabX and hoH genes. More detailed investigation on SyR1 showed that this sRNA is upregulated under high-light stress and CO₂ depletion [2] and that a strain overexpressing Syr1 exhibits a bleaching-phenotype lacking photosynthetic pigments. A bioinformatical target prediction identified a handful of potential mRNA targets including the 5'-UTR of slr1471 as well as photosynthesis genes like psaL and the cpc-operon transcript. Slr1471 encodes a conserved translocase of the Alb3/Oxal/YidC protein family which has a function in the integration of proteins into thylakoid membranes and assists in the assembly of photosystem complexes [4]. Preliminary gel mobility shift assays provide evidence for an interaction between SyR1 and a region around the Shine-Dalgarno sequence of slr1471 mRNA in vitro. Furthermore greatly reduced accumulation of the slr1471-transcript and the protein product could be observed in the SyR1 overexpressing strain implying a functional interaction in vivo. For these findings we speculate that SyR1-dependent gene regulation affects photosystem biosynthesis and homeostasis. Ongoing experiments aim to verify other predicted target mRNAs of SyR1, in particular by using high resolution microarrays.