MOLECULAR-CLONING, DNA-SEQUENCE AND TRANSCRIPTIONAL ANALYSIS OF THE RHODOSPIRILLUM-MOLISCHIANUM B800 X50 LIGHT-HARVESTING GENES/

The amino acid sequences of the B800/850 light-harvesting proteins fro m Rhodospirillum molischianum were determined by Edman degradation. On the basis of these amino acid sequences, two degenerated oligonucleot ides were synthesized and used for PCR of genomic DNA. The resulting 1 50 bp DNA fragment was cloned, sequenced and used for subsequent South ern blot analysis of digested genomic DNA. A 2.3 kbp EcoRI fragment st rongly hybridized to the probe and a size selected genomic library fro m genomic DNA was constructed. One clone scored positive during screen ing of the library with the PCR-fragment and subsequent DNA sequence a nalysis of the clone revealed the presence of three A-genes (A1A2A3) e ncoding alpha-polypetides and of two B-genes (B1B2) encoding beta-poly peptides of the B800/850 complex. The arrangement of the different gen es are B1A1, B2A2 and A3 where only B1 and B2 are preceded by typical Shine-Dalgarno sequences. In addition, typical nucleotide sequences fo r a rho-independent termination of transcription are located downstrea m of the genes A1 and A2. The deduced amino acid sequences revealed th at the a-genes encoded for identical polypeptides, whereas the deduced beta-polypeptides differed in their amino acid sequence at four posit ions. Transcriptional operon analysis revealed that the genes A1B1 and A2B2 are both dicistronically transcribed, whereas the gene A3 is not .