Figure 2.

Organization of the rbcS locus in C. reinhardtii (27). The coding regions of the rbcS1 and rbcS2 genes are displayed as exons (solid boxes) connected by introns (thick lines). Both genes are oriented in a 5′ to 3′ direction. A PstI restriction fragment used as a ³²P-labeled DNA probe is shown as an open box. PCR products, generated from both rbcS1 and rbcS2 with a single pair of oligonucleotides, are shown as hatched boxes. Restriction sites are indicated: R, EcoRI; H, HindIII; P, PstI; S, SacII. Each rbcS gene encodes a 185-residue polypeptide. The first 45 residues are removed during chloroplast import to form the 140-residue mature small subunits. Approximate locations of amino-acid differences between the two small subunits (residues 22, 47, 128, and 132) are marked with single-letter abbreviations within the exons: A, Ala; F, Phe; S, Ser; T, Thr; W, Trp.