Copyright The McGraw-Hill Companies,Inc.Permission required for reproduction or display Chapter 23 Transposition(转座 Stanley N.Cohen/Photo Researchers,Inc
Chapter 23 Transposition(转座)
23.1 Bacterial Transposons(转座子) Transposition,a transposable element, or transposon,moves from one DNA address to another
23.1 Bacterial Transposons (转座子) Transposition, a transposable element, or transposon, moves from one DNA address to another
Transposable elements in prokaryotes: Three examples: l.Insertion sequence(IS插入序列)elements 2.Transposons(Tn,转座子) 3.Bacteriophage Mu(Mu phage,转座噬菌体)
Transposable elements in prokaryotes: Three examples: 1. Insertion sequence (IS插入序列) elements 2. Transposons (Tn,转座子) 3. Bacteriophage Mu (Mu phage,转座噬菌体）
Discovery of Bacterial Transposons phage mutations the mutant genes contained long stretches of extra DNA. Phage Phage λ入(gal+) 入(gal-) gal-phage gal+phage lyticlytic(裂解)infection Ultracentrifuge Collect fractions explanation High Low density density foreign DNA had inserted into the gal gene and thereby mutated it.Indeed, nsertion later experiments revealed 800-1400- bp inserts in the mutant gal gene->insertion sequences (ISs)
Discovery of Bacterial Transposons phage mutations : the mutant genes contained long stretches of extra DNA. lyticlytic(裂解)infection foreign DNA had inserted into the gal gene and thereby mutated it. Indeed, later experiments revealed 800-1400- bp inserts in the mutant gal gene→insertion sequences (ISs). explanation :
Insertion Sequences(lSs,插入序列)： The Simplest Bacterial Transposons ISs contain only the elements necessary for transposition. 1.inverted terminal repeats (ITRs)at a transposon's ends,one of which is the inverted repeat of the other. 2.The set of genes(at least two)that code for the enzymes that catalyze transposition(transposase,转座酶). Insertion sequence,IS1 R Transposase gene IR 5'GGTGATGCTGCCAACTTACTGAT 3 5'ATCAATAAGTTGGAGTCATTACC 3 3 CCACTACGACGGTTGAATGACTA 5 3 TAGTTATTCAACCTCAGTAATGG 5
Insertion Sequences(ISs,插入序列): The Simplest Bacterial Transposons ISs contain only the elements necessary for transposition. 1. inverted terminal repeats (ITRs) at a transposon‘s ends, one of which is the inverted repeat of the other. 2.The set of genes(at least two)that code for the enzymes that catalyze transposition (transposase,转座酶)
插入序列(insertion sequence IS) 700— 2000 base pair (bp) GATCGTC-GACGATC CTAGCAG- -CTGCTAG R R GATCGTC -GACGATC Stem-loop 5'GATCGTC : 3'CTAGCAG
插入序列 （ insertion sequence IS ） ● GATCGTC -GACGATC l 700 2000 base pair （bp） IR IR GATCGTC -GACGATC CTAGCAG-CTGCTAG Stem-loop 5’ GATCGTC 3’ CTAGCAG
a plasmid containing a transposon Intemal genes Inverted terminal repeats Invertedterminal repeats ransposable element- Strand separation Intra-strand annealing GGGTCTG CAGA Plasmid DNA The DNA was shadowed with heavy metal and subjected to electron microscopy.The loop- stem-loop structure is obvious
a plasmid containing a transposon The DNA was shadowed with heavy metal and subjected to electron microscopy. The loopstem-loop structure is obvious
direct repeats(直接重复，同向重复) in the DNA immediately surrounding the transposon. IS 5 ACAGTTCAG CTGAACTGT 3 3 TGTCAAGTC GACTTGACA 5 R R Insertion of IS element into chromosomal DNA the transposase cuts the target Target site DNA in a staggered fashion ↓cut Chromosomal 5' TCGAT 3 DNA 3 AGCTA Cut Inserted IS element 5 TCGAT ACAGTTCAG CTGAACTGT 3 TGTCAAGTC GACTTGACA AGCTA 5 R R Gaps filled by DNA polymerase,DNA ligase New DNA Host DNA TCGAT ACAGTTCAG CTGAACTGT TCGAT 3 3 AGCTA TGTCAAGTC GACTTGACA AGCTA New DNA R R Host DNA Duplicated target site sequence
direct repeats(直接重复，同向重复） in the DNA immediately surrounding the transposon. the transposase cuts the target DNA in a staggered fashion
CopyrighThe MoGr-HCompanes Inc Parission reqrd or rpoduconory (a) CATAGCCTGAT GTATCGGACTA Target plasmid Cut at arrows (b) CATAGCCTGA G TATCGGACTA Insert transposon ( CATAGCCTGA G TATCGGACTA Fill in gaps ( CATAGCCTGA ATAGCCTGAT GTATCGGACT TATCGGACT A
小结 √插入序列是细菌转座子中最简单的一种。 √它只包含自身转座所必须的元件：末端的短 反向重复序列和至少两个编码完成转座所需 的转座酶的基因。 √转座过程包括目的DNA中的一个短序列的复 制；转座后在插入序列侧翼的每一侧都会有 这种短序列的拷贝
小结 ✓插入序列是细菌转座子中最简单的一种。 ✓它只包含自身转座所必须的元件：末端的短 反向重复序列和至少两个编码完成转座所需 的转座酶的基因。 ✓转座过程包括目的DNA中的一个短序列的复 制；转座后在插入序列侧翼的每一侧都会有 这种短序列的拷贝