Genome of Escherichia coli

E. coli is an important microorganism. It
colonizes the lower intestines of mammals including
man in a symbiotic relationship. Pathogenic
strains of E. coli cause gastrointestinal,
urinary, pulmonary, and nervous system infections
in humans. The E. coli genome has
4639221 bp. A total of 2657 protein-coding
genes with known function (62% of all genes)
and 1632 genes (38%) without known function
have been identified. The simplified figure
shows eight genes (A–H), the origin of replication
(ORI), and the genes for DNA polymerase
and methionine. Four operons are shown: the
operons for lactose consisting of three genes,
for galactose with four genes, for tryptophan
with five genes, and for histidine with nine
genes. About a fourth of all genes in E. coli are
organized into 75 different operons. Most genes
of the E. coli genome are present as a single
copy; only the genes for ribosomal RNA (rRNA)
are present in multiple copies. As a result, the
bacteria can double their protein content every
20 minutes during cell division.