Translation (Nguyen et al., 2003; Takano et al., 2003). Translational regulation is via a very rare UUA codon in the adpA mRNA, falling between the segments encoding the two domains of AdpA. UUA is the only one of the six leucine codons to comprise only A and U residues, so the corresponding TTA codon is comparatively rare in GC-rich genomes ?it occurs in only 147 chromosomal genes in S. coelicolo