四、 snRNP Particles snRNAs transcribed by rna pol li complex with specific protein to form SnRNP These rna are rich in uracil and are denoted as U、U2etc Ul、U2、U4、U5andU6 are those involved in pre-mRNA Splicing. Many others seem to be involved in determining the sites of methylation of pre-rrna and are located in the nucleolus
四、snRNP Particles snRNAs transcribed by RNA Pol II complex with specific protein to form snRNP. These RNA are rich in uracil and are denoted as U1、U2 etc. U1、U2、U4、U5 and U6 are those involved in pre-mRNA splicing. Many others seem to be involved in determining the sites of methylation of pre-rRNA and are located in the nulcleolus
The formation of SnRNP The snrNa are synthesized in nucleus by rna Pol ll and have a normal 5-cap. They are exported to the cytoplasm where they associate with the common core protein and other specific protein. Their 5-cap gains two methyl groups and they are then imported back into nucleus where they function in splicing
The formation of snRNP : The snRNA are synthesized in nucleus by RNA Pol II and have a normal 5’-cap. They are exported to the cytoplasm where they associate with the common core protein and other specific protein. Their 5’-cap gains two methyl groups and they are then imported back into nucleus where they function in splicing
五、 The procession of pre-mRNA 真核mRNA的加工一般要经过四步 (1)5加帽( (capping); (2)3加尾 ( tailing); (3)切除内含子( intron cleavage); (4)修饰( modification):对某些碱基进行 甲基化
五、The procession of pre-mRNA 真核mRNA的加工一般要经过四步： (1) 5′加帽(capping)； (2) 3′加尾(tailing)； (3) 切除内含子(intron cleavage )； (4) 修饰(modification)：对某些碱基进行 甲基化
15”- capping The 5'end is modified by addition of m'G residue, called a cap. The is nucleotide is added to the new transcript in the reversed orientation gIvIng5’-5 linkage. The sugars on the first and secondtranscribed nucleotides are methylated. m'GNmpNmp The transcripts are thus stabilized for preventing against 5-exonuclease digestion. The cap is also important for splicing, nuclear transport and translation
The 5’ end is modified by addition of m7G residue, called a cap. The is nucleotide is added to the new transcript in the reversed orientation, giving 5’-5’ linkage. The sugars on the first and secondtranscribed nucleotides are methylated. m7GNmpNmp The transcripts are thus stabilized for preventing against 5’-exonuclease digestion. The cap is also important for splicing, nuclear transport and translation. 1 5’-capping :
三种帽子的共同 位置 在和1中可被甲 GH,-o-P CH 帽1位置入CH3 帽2位置CH3 图13-mRNA5端的帽子位置和可被甲基化的位点
三种帽子的共同 在帽 1 中可被甲基化 NH2 位 置 C N O CH3 N C CH C N HC C HN C N N CH O C O O O 2HN N N CH2 O P O P O P O CH O O O 帽 1 位置 OCH3 O O P O CH2 O 帽 2 位置 OCH3 O O P O O 图 13- mRNA 5’ 端的帽子位置和可被甲基化的位点