Cloning the Gene for Cytochrome C₂ from Rhcdospirillum Rubrum

Abstract

Cytochrome c2 of Rhodos pirillum rubrum, a purple non-sulphur bacterium, is involved in the photosynthetic electron transport chain, and being the final component of the pathway, it donates electrons back to the bacterial photochemical reaction centre. The redox potentials of the various components in the electron transport system are critical to the electron flow, and are thought to be determined in part by the protein environment of the heme prosthetic groups. The crystal structure of c2 has been resolved to 2A resolution (Salemme et al, 1973) and recently the structure of the reaction centre complex of Rhodobacter sphaeroides has been determined (Allen et al, 1987). This system is therefore well suited to a detailed study by protein engineering. Although the amino acid sequence of c2 has been known for a long time (Dus et al, 1968), the DNA sequence is as yet unknown. The cloning strategy employed to isolate the cytochrome c2 gene (designated cycA) from R.rubrum is described below.