FIG. 4.

Confirmation of the mtmB sequence containing the in-frame UAG codon. The figure illustrates the regions that were cloned or amplified by PCR from M. barkeri genomic DNA and sequenced. λ-SAB29 is the original phage clone in which the amber codon was first observed. Nucleotide numbers are the same as those in Fig. 1. pSAB21 is a pUC19 derivative which contains the indicated 1.1-kb SacI-HindIII fragment cloned directly from M. barkeri MS genomic DNA. PCR-MS and PCR-NIH are fragments amplified from M. barkeri MS or NIH genomic DNA and directly sequenced.