Studies on the Function of The pufQ Gene Product in Bacteriochlorophyll Biosynthesis

Abstract

The pufQ gene is an open reading frame, located between an oxygen-regulated promoter region and the pufB gene (which codes for the B870β light-harvesting protein, in the puf operon of Rhodobacter capsulatus 1,2 and Rhodobacter sphaeroides.3 Evidence has accumulated in a number of laboratories that expression of the pufQ gene is required for normal levels of bacteriochlorophyll (Bch1) biosynthesis. The pufQ gene was shown to employ frequently used codons and to be induced by the same environmental factors which led to the induction of the other known puf genes.1 Although strains from which the entire puf operon had been deleted were still able to form some Bchl (appearing in the form of the B800-850 [LHII] complex), restoration of the pufQ gene in trans greatly increased Bchl synthesis.4,5 In addition, Bauer and Marrs4 have found that the amount of Bchl produced was directly proportional to the amount of the pufQ gene product expressed. These experiments were performed in strains of R. capsulatus genetically manipulated to first remove the puf operon, and then insert the pufQ gene on a plasmid in which its transcription could be regulated by the nature of the nitrogen source. It is not known, however, where the pufQ gene product (or Q-protein) exerts its effect. Bauer and Marrs4 have shown that the expression of pufQ does not appear to regulate the transcription (or translation) of bch genes. Other possibilities, however, include: activation of the bch gene products (the biosynthetic enzymes), activation of their substrates (magnesium tetrapyrrole intermediates), transport of intermediates into (or across) biomembranes, or regulation of the assembly of light-harvesting (LH) and/or reaction center (RC) Bch1-protein complexes.