Influences on gene expression in vivo by a Shine-Dalgarno sequence.

• The Shine-Dalgarno (SD+: 5'-AAGGAGG-3') sequence anchors the mRNA by basepairing to the 16S rRNA in the small ribosomal subunit during translation initiation. We have here comparedhow an SD+ sequence influences gene expression, if located upstream or downstream of an initiation codon.The positive effect of an upstream SD+ is confirmed. A downstream SD+ gives decreased gene expression.This effect is also valid for appropriately modified natural Escherichia coli genes. If an SD+ is placedbetween two potential initiation codons, initiation takes place predominantly at the second start site.The first start site is activated if the distance between this site and the downstream SD+ is enlargedand/or if the second start site is weakened. Upstream initiation is eliminated if a stable stem-loopstructure is placed between this SD+ and the upstream start site. The results suggest that the two startsites compete for ribosomes that bind to an SD+ located between them. A minor positive contribution toupstream initiation resulting from 3' to 5' ribosomal diffusion along the mRNA is suggested. Analysisof the E. coli K12 genome suggests that the SD+ or SD-like sequences are systematically avoided in theearly coding region suggesting an evolutionary significance.

Ämnesord

NATURVETENSKAP  -- Biologi -- Biokemi och molekylärbiologi (hsv//swe)

NATURAL SCIENCES  -- Biological Sciences -- Biochemistry and Molecular Biology (hsv//eng)

Nyckelord

Base Sequence

Binding Sites

Codon; Initiator/genetics/metabolism

Escherichia coli/*genetics/metabolism

Gene Expression Regulation; Bacterial

Genes; Bacterial/genetics

Genes; Reporter

Molecular Sequence Data

Nucleic Acid Conformation

Protein Biosynthesis/*genetics

RNA; Bacterial/metabolism

RNA; Messenger/metabolism

RNA; Ribosomal; 16S/metabolism

RNA; Transfer; Amino Acyl/chemistry/metabolism

Ribosomes/*metabolism

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