ABSTRACT
An RNA degrading, high molecular weight complex was purified from Rhodobacter capsulatus. N-terminal sequencing, glycerol-gradient centrifugation, and immunoaffinity purification as well as functional assays were used to determine the physical and biochemical characteristics of the complex. The complex comprises RNase E and two DEAD-box RNA helicases of 74 and 65 kDa, respectively. Most surprisingly, the transcription termination factor Rho is a major, firmly associated component of the degradosome.
Subject(s)
RNA, Messenger/metabolism , Rhodobacter capsulatus/metabolism , Amino Acid Sequence , Antibodies/immunology , Cell Fractionation , Centrifugation/methods , Endoribonucleases/immunology , Endoribonucleases/metabolism , Macromolecular Substances , Molecular Sequence Data , Precipitin Tests , RNA Helicases/metabolism , RNA Processing, Post-Transcriptional , Rhodobacter capsulatus/chemistry , Rhodobacter capsulatus/genetics , Sequence Analysis, ProteinABSTRACT
The transcription of genes encoding pigment binding proteins in the facultative photosynthetic bacterium Rhodobacter capsulatus is regulated in response to oxygen partial pressure. Previous results identified RegA and RegB as members of a two component system involved in oxygen dependent synthesis of the photosynthetic apparatus. Here we demonstrate that RegA differentially controls the transcription of the puf and pucoperons which encode proteins of the LHI and LHII antenna complexes, respectively. In a regA mutant strain the level of puf specific mRNA reaches about 30% of the wild type levels and transcription is still responsive to oxygen tension. In contrast, the level of puc specific mRNA is very low and is no longer oxygen regulated. RegA binds to DNA sequences upstream of both the puf and puc operons, although with different affinities. We provide experimental evidence that a putative helix-turn-helix motif in the C-terminal region of RegA is responsible for its specific binding to the puf and puc promoter regions. In contrast to many other response regulators, the affinity of RegA for the target DNA is only slightly modified by phosphorylation.
Subject(s)
Bacterial Proteins/metabolism , DNA, Bacterial/metabolism , DNA-Binding Proteins/metabolism , Photosynthetic Reaction Center Complex Proteins/genetics , Rhodobacter capsulatus/metabolism , Bacterial Proteins/genetics , Base Sequence , DNA, Bacterial/genetics , DNA-Binding Proteins/genetics , Gene Expression , Genes, Bacterial , Molecular Sequence Data , Mutation , Operon , Rhodobacter capsulatus/geneticsABSTRACT
The formation of the photosynthetic apparatus in Rhodobacter capsulatus is regulated by oxygen tension. Previous studies have shown a regulatory effect of oxygen on the transcription of photosynthesis genes and on the stability of certain mRNA segments. Here we show that oxygen affects puf and puc gene expression posttranslationally and that this regulation depends on the presence of bacteriochlorophyll. Our data suggest that this posttranslational effect of oxygen on puf and puc expression is due to the primary effect of oxygen on bacteriochlorophyll synthesis or assembly of pigment protein complexes. Oxygen does not affect the rates of translation of puf-encoded proteins.
