| Čoahkkáigeassu: | <p>Several noncoding RNAs potentially involved in nitrogen (N)-regulation have been detected in <em>Methanosarcina mazei</em>, however, targets have been identified only for one of them. Here, we report on the function of sRNA<sub>41</sub>, highly expressed under N-sufficiency. Comprising 120 nucleotides, sRNA<sub>41</sub> shows high sequence and structural conservation within draft genomes of numerous <em>Methanosarcina</em> species. <em>In silico</em> target prediction revealed several potential targets, including genes of two homologous operons encoding for acetyl-CoA-decarbonylase/synthase complexes (ACDS) representing highly probable target candidates. A highly conserved single stranded region of sRNA<sub>41</sub> was predicted to mask six independent ribosome binding sites of these two polycistronic mRNAs and was verified <em>in vitro</em> by microscale thermophoresis. Proteome analysis of the respective sRNA<sub>41</sub>-deletion mutant showed increased protein expression of both ACDS complexes in the absence of sRNA<sub>41</sub>, whereas no effect on transcript levels was detected, arguing for sRNA<sub>41</sub>-mediated post-transcriptional fine-tuning of ACDS expression. We hypothesize that the physiological advantage of downregulating sRNA<sub>41</sub> under N-limiting conditions is the resulting increase of ACDS protein levels. This provides sufficient amounts of amino acids for nitrogenase synthesis as well as reducing equivalents and energy for N<sub>2</sub>-fixation, thus linking the carbon and N-metabolism.</p>
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