Transcript levels of the ORFs upstream of the hyp -genes in Nostoc sp. strain PCC 7120 after nitrogen depletion. Agarose gels showing the amplified PCR products using cDNA prepared RNA from Nostoc PCC 7120 cultures 0, 24, 48 and 72 hours after nitrogen depletion as well as isolated heterocysts 48 hours after nitrogen depletion. The tested genes are the hydrogenase and ribosome structural genes hupS and 23S, the hyp-genes hypC and hypF and the ORFs upstream of the hyp-genes (asr0689, asr0690, alr0691, alr0691 and alr0693). All DNA fragments were amplified with PCR using 30 cycles, except for nifD and 23S where 25 and 15 cycles were used, respectively. Negative (-) and positive controls (+) for the PCR reactions are shown.