ENDONUCLEOLYTIC DEGRADATION OF PUF MESSENGER-RNA IN RHODOBACTER-CAPSULATUS IS INFLUENCED BY OXYGEN

The formation of pigment-protein complexes in facultatively photosynthetic bacteria is regulated by the oxygen tension in the culture. It is shown that the degradation of some mRNA species encoding components of the photosynthetic apparatus is affected by oxygen. The puf mRNA segment, encoding the pigment-binding proteins of the reaction center, and the 0.5-kb puc mRNA species, encoding pigment-binding proteins of the light-harvesting LHII antenna complex of Rhodobacter capsulatus were degraded more rapidly under high oxygen tension than under low oxygen tension. Studies on strains having deletions or insertions in the puf operon indicate that rate-limiting endonucleolytic cleavage in the reaction center coding region of the polycistronic puf mRNA was influenced by growth conditions. However, other mRNA segments, for which exonucleolytic degradation was postulated to be rate-limiting, decayed with the same rate under either high or low oxygen tension. Likewise, the degradation of the puhA mRNA, the cycA mRNA, and the cytfbc mRNA was found to be independent of the oxygen tension in the culture. The data strongly suggest that specific mRNA sequences or structures are responsible for the observed oxygen effect on mRNA stability.