초록
<P>The ethylene-forming enzyme (EFE) from <I>Pseudomonas syringae</I> catalyzes the synthesis of ethylene which can be easily detected in the headspace of closed cultures. A synthetic codon-optimized gene encoding N-terminal His-tagged EFE (EFEh) was expressed in <I>Synechocystis</I> sp. PCC 6803 (<I>Synechocystis</I>) and <I>Escherichia coli</I> (<I>E. coli</I>) under the control of diverse promoters in a self-replicating broad host-range plasmid. Ethylene synthesis was stably maintained in both organisms in contrast to earlier work in <I>Synechococcus elongatus</I> PCC 7942. The rate of ethylene accumulation was used as a reporter for protein expression in order to assess promoter strength and inducibility with the different expression systems. Several metal-inducible cyanobacterial promoters did not function in <I>E. coli</I> but were well-regulated in cyanobacteria, albeit at a low level of expression. The <I>E. coli</I> promoter P<SUB>trc</SUB> resulted in constitutive expression in cyanobacteria regardless of whether IPTG was added or not. In contrast, a Lac promoter variant, P<SUB>A1lacO-1</SUB>, induced EFE-expression in <I>Synechocystis</I> at a level of expression as high as the Trc promoter and allowed a fine level of IPTG-dependent regulation of protein-expression. The regulation was tight at low cell density and became more relaxed in more dense cultures. A synthetic quorum-sensing promoter system was also constructed and shown to function well in <I>E. coli</I>, however, only a very low level of EFE-activity was observed in <I>Synechocystis</I>, independent of cell density.</P>