The 6S RNA is a global transcriptional riboregulator, which is exceptionally widespread among most bacterial phyla. While its role is already well-characterized in heterotrophic bacteria, we subjected a cyanobacterial homolog to functional analysis, thereby extending the scope of 6S RNA action to the special challenges of photoautotrophic lifestyles. This study reveals 6S RNA as an integral part of the cellular response of Synechocystis sp. PCC 6803 to changing nitrogen availability. Physiological characterization of a 6S RNA deletion strain (ΔssaA) demonstrates a delay in the recovery from nitrogen starvation. Significantly decelerated phycobilisome reassembly and glycogen degradation is accompanied with reduced photosynthetic activity compared to the wild type. Transcriptome profiling further revealed that predominantly genes encoding components of both photosystems, ATP synthase and the phycobilisomes were negatively affected in the ΔssaA mutant. In vivo pull-down studies of the RNA polymerase complex further indicate a promoting effect of 6S RNA on the recruitment of the cyanobacterial housekeeping sigma factor SigA, concurrently supporting dissociation of group II sigma factors during recovery from nitrogen starvation. According to these results, 6S RNA supports a rapid adaptation to changing nitrogen conditions by regulating the switch from group II sigma factors SigB / SigC to SigE / SigA dependent transcription. We performed microarray analysis of total RNA from wild-type and ?ssaA cultures that were starved for nitrogen for seven days and recovered over a period of 48 hours. Sampling time points were t1 = 1h +N, t2 = 4h +N and t3 = 22h +N after nitrogen recovery. Samples were taken in biological replicates.