RESUMO
Repeat sequence exists in almost all organism genomes. Enterobacterial Repetitive Intergenic Consensus (ERIC), also named Intergenic Repetitive Unit (IRU), is a kind of intergenic repetitive sequence that exists predominantly in Enterobacteria. ERIC (IRU) was firstly discovered in Escherichia coli, followed by identification in many other bacteria. ERIC (IRU) is 127 bp long, and some with inserted sequences. Most ERIC (IRU) can be transcribed, and mRNA forms a stem-loop structure. ERIC (IRU) is restricted to transcribed regions of the genome, either in intergenic regions of polycistronic operons or in untranslated regions upstream or downstream of open reading framesn (ORF). ERIC (IRU) probably modulates the expression of flanking genes. ERIC (IRU) is highly conserved, for either its variation is restricted by the natural selection pressure, or it's "selfish DNA". ERIC-PCR described by Versalovic et al. can efficiently analyze the variation of different ecological systems and monitor the development of microbial flora of the same ecological system. In recent years, this technology has been applied to study the microbial population of animal intestinal tract.