Long range supra-organisation of the bacterial photosynthetic unit: archetype or artefact ?

Abstract

The hypothesis that the small hydrophobic protein Puf X induces the formation of arrays of core complexes in Rhodobacter sphaeroides (Frese et al. 2000) was advanced on the basis of linear dichroism (LD) data from a mutant of Rb. sphaeroides (LH2-LH1-RC-X-) complemented with plasmid-borne genes for the Light-Harvesting 1 complex and the Reaction Centre, with and without puf X. The use of a multi-copy plasmid raises the possibility of an excess of core complexes, with respect to the other components of the respiratory chain, being present in the intracytoplasmic membrane. This system differs markedly from the wild type where there is only one copy of the puf operon and which also has the puc operon present. To test our hypothesis further we have examined the LD properties of membranes from a mutant, DBCW G, that has only a single genomic copy of the puf operon (LH2-LH1+RC+X+). We have also compared true WT membranes with `pseudo¿ WT membranes, generated by complementing the puf deletion mutant, DPF2R (LH2+LH1-RC-X-), with the plasmid-borne puf operon. The properties of these membranes are reported.