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The Shine-Dalgarno (SD) sequence is a ribosomal binding site in prokaryotic messenger RNA, generally located around 8 bases upstream of the start codon AUG.〔 The RNA sequence helps recruit the ribosome to the mRNA to initiate protein synthesis by aligning the ribosome with the start codon. The Shine-Dalgarno sequence exists both in bacteria and archaea. It is also present in some chloroplast and mitochondrial transcripts. The six-base consensus sequence is AGGAGG; in ''Escherichia coli'', for example, the sequence is AGGAGGU, while subsequence GAGG dominates in ''E. coli'' virus T4 early genes. The Shine-Dalgarno sequence was proposed by Australian scientists John Shine (b. 1946) and Lynn Dalgarno (b. 1935). ==The 3' terminus of the small ribosomal RNA and the recognition of translation start sites in prokaryotic mRNA == Using a stepwise degradation and terminal labelling procedure developed by Hunt,〔Hunt J A (1970) Terminal-sequence studies of high-molecular-weight ribonucleic acid. The 3'-termini of rabbit reticulocyte ribosomal RNA. ''Biochemical Journal''. 120, 353-363.〕〔Shine J, Dalgarno L (1973) Occurrence of heat-dissociable ribosomal RNA in insects: the presence of three polynucleotide chains in 26S RNA from cultured Aedes aegypti cells. Journal of Molecular Biology, 75, 57-72.〕 Shine and Dalgarno showed that the nucleotide tract at the 3' terminus of ''E. coli'' 16S ribosomal RNA (rRNA) is pyrimidine-rich and has the sequence -PyACCUCCUUA 3' OH . They proposed that this stretch of nucleotides recognises a complementary purine-rich sequence (AGGAGGU) in the region upstream of the correct initiator AUG found in the ribosome binding sites of a variety of coliphage mRNAs (Ref 1). The 3' terminal sequences of 16S rRNA from ''Pseudomonas aeruginosa'', ''Bacillus stearothermophilus'' and ''Caulobacter crescentus'' are also pyrimidine-rich, but differ one from the other and from the ''E.coli'' sequence. On the basis of complementarity relationships between these sequences and the purine-rich sequence in the ribosome binding site of different bacterial mRNA species it was proposed that the precise sequence at the 3'-end of the rRNA determines the intrinsic capacity of the prokaryotic ribosome to translate a particular cistron in a mRNA.〔Shine J, Dalgarno L (1975) Determinant of cistron specificity in bacterial ribosomes. ''Nature ''254 (5495) 34-38.〕 The specific base pairing between the 3'-end of the rRNA and the sequence preceding an initiator AUG provides a mechanism by which the cell can distinguish between initiator AUGs and internal and/or out-of-phase AUG sequences. The degree of base pairing also plays a role in determining the rate of initiation at different AUG initiator codons in polycistronic mRNAs. This hypothesis was strengthened by the demonstration that ''E.coli'' ribosomes use base pairing to identify start sites for translation of bacteriophage mRNA.〔Steitz J A, Jakes K (1975) How ribosomes select initiator regions in mRNA: base pair formation between the 3'-terminus of 16S rRNA and the mRNA during the initiation of protein synthesis in Escherichia coli. Proc Nat Acad Sci USA 72, 4734-4738.〕 This study took advantage of the antibiotic colicin E3 which induces the rapid shut down of protein synthesis in susceptible ''E.coli'' due to the removal of about 50 nucleotides from the 3'-end of 16S RNA as a result of a single endonucleolytic cleavage.〔Bowman CM, Dahlberg JE, Ikemura T, Konisky J, Nomura M. (1971) Specific inactivation of 16S ribosomal RNA induced by colicin E3 in vivo. Proc Nat Acad Sci, USA 68, 964-968.〕〔Konisky J, Nomura M (1967) Interaction of colicins with bacterial cells. II. Specific alteration of Escherichia coli ribosomes induced by colicin E3 in vivo. J. Mol Biol, 26, 181-195.〕 Using colicin E3, a hydrogen bonded mRNA-rRNA complex was isolated after the formation of initiation complexes between ''E.coli'' ribosomes and a phage R17 initiator region. This complex included the last 50 nucleotides of 16S rRNA and melted at a temperature consistent with the predicted structure (Ref 5). Many studies have confirmed that base pairing between the SD sequence in mRNA and the 3' end of 16S rRNA is of prime importance for initiation of translation by bacterial ribosomes.〔Dahlberg A E (1989) The functional role of ribosomal RNA in protein synthesis. ''Cell'' 57, 525-529.〕 The level of 3'-terminal adenylation of ''Ps. aeruginosa'' 16S rRNA is a function of bacterial growth rate.〔Shine J, Dalgarno L (1975) Growth dependant changes in terminal heterogeneity involving 3'-adenylate of bacterial 16S ribosomal RNA. ''Nature'' 256, 232-233.〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Shine-Dalgarno sequence」の詳細全文を読む スポンサード リンク
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