2 核苷酸的切除修复.ppt

The human BER pathway. (Source: Robert F. Weaver, Molecular Biology) The human BER pathway (Source: Robert F. Weaver, Molecular Biology) (a) Spontaneous cytosine deamination has converted a C (blue) to a U (orange) in the lower strand of the DNA. (b) A glycosylase removes the uracil. (c) Human apurinic/apyrimidinic (AP) endonuclease (APE1) cleaves on the 5′-side of the apyrimidinic site. (d) DNA polymerase β correctly fills in the gap with a C (blue) and simultaneously removes the hanging sugar-phosphate tag (green). (e) DNA ligase I seals the nick, returning the DNA to normal. (f) Occasionally, the DNA polymerase makes a mistake. This time it has incorporated a T (red) rather than a C, leaving a mismatch at the 3′-end of the fragment to the left of the nick. (g) APE1 uses its 3′-exonuclease to remove the mispaired T, again leaving a gap. (h) This time, DNA polymeraseβ correctly places a C (blue) across from the G. Now the mismatch is repaired, and the DNA just needs to be ligated to be back to normal. 1.DNA糖苷酶：识别DNA中的不正常碱基，将其水解脱落。 尿嘧啶-N-糖苷酶 次黄嘌呤-N-糖苷酶 2.无嘌呤或无嘧啶位点称为AP-位点 AP核酸内切酶 3. 外切核酸酶 4. DNA聚合酶I 2. 核苷酸的切除修复( Nucleotide excision repair, NER) DNA双螺旋结构有较大损伤时。 ①首先由切除酶识别DNA的损伤位点，在损伤部位的两侧切开磷酸二酯键。 ②在DNA聚合酶的催化下，以完整的互补链为模板，按5’-3’方向DNA链，填补已切除的空隙。 ③由DNA连接酶将新合成的DNA片段与原来的DNA链连接起来。 大肠杆菌核苷酸切除修复有关的酶 1） UvrABC内切酶（切除酶）： 是uvrA，uvrB和uvrC三个基因表达产物的复合物；在损伤位置两侧各作一缺口（UvrB在3’端，UvrC在5’端）。 2）解螺旋酶（UvrD编码）：去除UvrABC内切酶产生的寡核苷酸； 3）DNA聚合酶(DNA pol) 4）DNA连接酶(DNA Ligase) Nucleotide excision repair in E. coli (Source: Robert F. Weaver, Molecular Biology) Nucleotide excision repair in E. coli (a) The UvrABC excinuclease cuts on either side of a bulky damaged base (red). This causes removal (b) of an oligonucleotide 12 nt long. If the damage were a pyrimidine dimer, then the oligonucleotide would be a 13-mer instead of a 12-mer. (c) DNA polymerase I fills in the missing nucleotides, using the top strand as template, and then DNA ligase seals the nick to co