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promoters in Ecoli DNA - (Aug/31/2005 )


I wonder if all of the for example 4253 coding regions in DNA sequence of Ecoli k12 have a promoter region like TA box or only some of them have a promoter?



Unlike eukaryotic systems, prokaryotes typically have poly-cistronic messages -- messenger RNA carrying more than one coding region. A promoter is only necessary upstream of the first gene in an "operon" which might contain one to dozens of genes. Often, but not always, the genes in an operon are functionally related, and are regulated as a group. Prokaryotic promoters typically are much shorter and simpler than eukaryotic promoters, and typically are controlled more by repressors than by enhancers. The most common promoters in E. coli contain a -35 sequence, concensus TTGACA, and a -10 sequence, concensus TATAAT, separated by 17 bp. A TG is often found in this region, the so-called -16 sequence.