Gene expression analysis RT-PCR results are shown for nitrogen-fixing and non-nitrogen-fixing conditions. The PCR generated DNA products were visualized by agarose gel electrophoresis. From the left to the right the four individual lanes on each agarose gel represent: 1) RT-PCR product demonstrating the transcription of the hydrogenase maturating peptidases (hoxW/hupW) and their respective hydrogenase large subunits (hoxH/hupL). 2) Control, where DNA instead of the cDNA sample from the RT reaction from the respective strain were used in the PCR reaction. 3) Control, with no reverse transcriptase enzyme added to the RT reaction. 4) Control, where dH2O instead of the cDNA sample from the RT reaction was added to the PCR reaction tube. Product sizes are shown in Table 4. Diffuse bands originate from primer-dimers artifacts. Nostoc punctiforme: Nostoc punctiforme ATCC 29133/PCC 73102.