29 separated by an intervening stretch of DNA, variable in length depending on the particular species of origin (Curtis & Hazelkorn, 1983; Shinozaki & Sugiura, 1983). The gene from S,.rzc~c.lioc.oc~r~us PCC30 1 (Reichelt & Delaney, 1983) has been cloned into the ampr region of PLa2311 (Remaut ct al., 1981) with expression controlled by the strong temperature-sensitive leftward promoter (PI) of bacteriophage EL (Gatenby et al., 1985). The construct is expressed in E. coli host organisms and produces active Rubisco. At present the levels of enzyme are poor, with low specific activity, possibly due to an under-production of the S-subunit. However, the synthesis of an active, multisubunit enzyme in non-photosynthetic bacteria argues against the necessity of a complicated assembly mechanism for Rubisco from cyanobacteria. Better constructs are certain to be developed that can be manipulated by 'in vitro' techniques and produce large amounts of enzymes. These will then be exploited to determine the structural basis for the differences between Rubisco from diverse photosynthetic organisms and indicate ways of changing the partition coefficient of the bisphosphate substrate.