The SCO1 mutational map. SCO1 encodes for a predicted protein with a high degree of similarity to an EF-G containing a chloroplast localization signal (At1g62750). The locations of the 4 mutant alleles are indicated. The EMS-mutagenized sco1-1 allele represents a G to A base change within the GTP-binding domain of the gene, which converts a glycine at amino acid 132 to an arginine. The other alleles [sco1-2 (Salk_046154), sco1-3 (Salk_039084), and sco1-4 (Salk_025112)] were isolated from the Salk T-DNA insert collection.