DNA sequence and analysis of 136 kilobases of the Escherichia coli genome: organizational symmetry around the origin of replication

Abstract

The DNA sequence of a 136-kb segment (81.5 to 84.5 min) from the Escherichia coli origin of replication region has been determined and analyzed. Of the 122 protein coding regions that were found, we could assign no gene name or function to half of them, even in this well-studied part of the genome. The newly sequenced region also includes five RNA genes. The arrangement of open reading frames and potential promoters suggests 63 transcription units. The sequence was also analyzed for bend sites and two types of repeated sequence elements. Together with our sequence of the 84.5 to 86.5 min region, this new determination forms a 227-kb contiguous region centered on oriC. A global analysis of this region reveals a remarkable symmetry: most genes are transcribed divergently from the replication origin, and Chi octanucleotide (5'GCTGGTGG3') recombinational hot spots are also strikingly oriented with respect to the directions of replication and translation.