Construction of a gene bank and identification of the ribulose bisphosphate carboxylase/oxygenase genes from the nutritionally versatile cyanobacterium Chlorogloeopsis fritschii

Ribulose bisphosphate carboxylase in algae: synthesis, enzymology and evolution

Studies demonstrating differences in chloroplast structure and biochemistry have been used to formulate hypotheses concerning the origin of algal plastids. Genetic and biochemical experiments indicate that significant variation occurs in ribulose-1,5-bisphosphate carboxylase (Rubisco) when supertaxa of eukaryotic algae are compared. These differences include variations in the organelle location of the genes and their arrangement, mechanism of Rubisco synthesis, polypeptide immunological reactivity and sequence, as well as efficacy of substrate (ribulose bisphosphate and CO2) binding and inhibitor (6-phosphogluconate) action. The structure-function relationships observed among chromophytic, rhodophytic, chlorophytic and prokaryotic Rubisco demonstrate that: (a) similarities among chromophytic and rhodophytic Rubisco exist in substrate/inhibitor binding and polypeptide sequence, (b) characteristic differences in enzyme kinetics and subunit polypeptide structure occur among chlorophytes, prokaryotes and chromophytes/rhodophytes, and (c) there is structural variability among chlorophytic plant small subunit polypeptides, in contrast to the conservation of this polypeptide in chromophytes and rhodophytes. Taxa-specific differences among algal Rubisco enzymes most likely reflect the evolutionary history of the plastid, the functional requirements of each polypeptide, and the consequences of encoding the large and small subunit genes in the same or different organelles.

Insertion sequence IS2 in the cyanobacterium Chlorogloeopsis fritschii

A cloned DNA fragment, previously demonstrated to encode ribulose bisphosphate carboxylase/oxygenase (RuBisCO) of Chlorogloeopsis fritschii strain CCAP1411/1b, is shown also to include the entire transposable element, IS2, normally a resident in the Escherichia coli genome. Southern-blot hybridisation experiments confirm the presence of IS2 in the C. fritschii genome. This finding adds a new and unrelated species to the known host range of this element and provides evidence of genetic transfer between the Gram-negative E. coli and cyanobacteria. This may also have significance in relation to the nucleotide sequence rearrangements known to occur adjacent to RuBisCO and nif genes in other nitrogen-fixing cyanobacteria.