基因组学-5,6-2008演示教学.ppt

Transposition mechanisms of LINE and SINE LINE：LINE with full length contains DNA endonuclease and reverse transcriptase gene. 通过切开靶位点双链，提供了引物末端。 反转录转座子作为模板合成cDNA SINE：transposed by “borrowing” enzymes from other autonomous retroelements. Example of SINE in human genome—Alu Size：about 300bp Copy number: over 1 million，about 13% of whole genome. Structure: Dimer of processed pseudogene of 7SL RNA (including internal promoter recognized by RNA polymerase III) with 3’-polyA tail. 元件两侧为正向靶重复序列(target site duplications,TSD)。 Distribution: Most of them are located in intergenic space and intron sequences. About 1 Alu/ 5kbDNA. The length and sequence of Alu show polymorphism among individuals. Non-autonomous retroelement. Example of LINE in human genome—L1 Size：6.1kb of full length. Over 95% of L1s in human genome are transpositionally inert with deletions or rearrangements. Copy number：about 516000, 21% of human genome Distribution：concentrated in regions with lower GC content Structure： Contains ORF1 and ORF2 (N-end with ENdonuclease domain, C-end with Reverse Transcriptase domain). 5`UTR contains promoter and 3`UTR contains polyA tail. 元件两侧为正向靶重复序列(target site duplications,TSD) Autonomous retroelement. L1 activity proceeds as follows RNA polymerase II transcribes the L1 DNA into RNA. The RNA is translated by ribosomes in the cytoplasm into the proteins. The proteins and RNA join together and reenter the nucleus. The endonuclease cuts a strand of target DNA, often in the intron of a gene. The reverse transcriptase copies the L1 RNA into L1 DNA which is inserted into the target DNA forming a new L1 element there. A mass of retroelements in maize genome According to the endosymbiont theory, chloroplasts may origin from ( ). Cyanobacteria Rickettsia Yeast Virus Which of the following states about psuedogenes are right? ( ) Terminators may exist in conventional psuedogenes. Generally speaking, processed psuedogene cannot be transcribed because they lack o