Slot-blot transcript analysis of the genes encoding the first putative enzymes of the L-arginine deiminase pathway ( sll1336 ), the L-arginine oxidase/dehydrogenase pathway ( slr0782 ), and the L-arginine decarboxylase pathway (three possible deiminase-encoding genes: sll1683 , sll0662 , and slr1312 ) in Synechocystis sp. PCC 6803. Synechocystis sp. PCC 6803 cells were grown for 24, 48, or 72 h with nitrate or L-arginine as sole N-source and with a constant illumination of 50 μmol photons m-2 s-1. Steady state transcript pools were investigated with gene-specific probes of equal length and equal GC % content to assure equal labeling with Dig-dUTP. An rnpB-specific probed was used to assure equal loading. The figure allows for a direct comparison of the various transcript concentrations. Moreover, changes in transcript level can be compared in cells grown with L-arginine (increase or decrease) to that grown with nitrate.