PROTEINS ENCODED BY THE ESCHERICHIA-COLI REPLICATION TERMINUS REGION

The replication terminus region (31 to 35 min) of the Escherichia coli chromosome contains very few mapped genes (two per min) compared with the remainder of the chromosome, and much of the DNA appears dispensable. In order to determine whether, despite this, the terminus region consists of protein-coding sequences, we cloned 44 kb (1 min) of terminus region DNA (that surrounding trg at 31.4 min) and examined its ability to catalyze protein synthesis in vitro or in minicells. We were able to account for more than half the coding capacity of the cloned DNA with proteins synthesized in these systems, indicating that the sparsity of mapped genes in the terminus region does not result from a lack of identifiable coding sequences. We can therefore conclude that the terminus region is composed mainly of expressable, albeit inessential, protein-encoding genes.