SINGLE CORE POLYPEPTIDE IN THE REACTION-CENTER OF THE PHOTOSYNTHETIC BACTERIUM HELIOBACILLUS-MOBILIS - STRUCTURAL IMPLICATIONS AND RELATIONS TO OTHER PHOTOSYSTEMS

The gene for a reaction center core polypeptide from the anoxygenic ph otosynthetic bacterium Heliobacillus mobilis was cloned and sequenced. The deduced amino acid sequence consists of 609 residues with a molec ular mass of 68 kDa. An adjacent open reading frame is not transcribed under our experimental conditions. No evidence for a second related r eaction center core gene was found. The primary sequence of the reacti on center protein (P800 protein) shows a high percentage of sequence i dentity to photosystem I in a cysteine-containing loop, which is the p utative binding site of the iron-sulfur center F(X) and in the precedi ng hydrophobic region. Our data imply a homodimeric organization of th e reaction center. This is fundamentally different from photosystem I and most other photosynthetic reaction centers, where the reaction cen ter core is composed of two similar but nonidentical subunits.