FIG. 3.
(A) Restriction map of the 3.2-kb HindIII DNA fragment of the S. thermophilus ATCC 19258 chromosome. The thymidylate synthase gene (thyA-St) and the dihydrofolate reductase gene (dhfr-St) were deduced from the nucleotide sequence. A heavy line indicates a DNA fragment amplified by PCR with primers 84 and 86 containing the thyASt gene. (B) Restriction map of the 2.6-kb BamHI DNA fragment of the L. delbrueckii subsp. bulgaricus M-878 chromosome and the deduced thyALb and dhfrLb products. A heavy line indicates a DNA fragment amplified by PCR with primers 89 and 90 containing thyALb. A potential promoter (P), a potential terminator (T), and relevant restriction enzyme sites are indicated. aa, amino acids.