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第三节 mRNA Processing, hnRNPs and snrNps 一、 hnrNa 二、pre- mRNAS 三、 hnrNP 四、 SnRNPs 五、pre- mRNA processing
第三节 mRNA Processing, hnRNPs and snRNPs 一、 hnRNA 二、 pre-mRNAs 三、 hnRNP 四、 snRNPs 五、pre-mRNA processing
hnrna Eucaryotic rNa Pol Il transcribes a variety of different genes, from snrna genes of 60-300nt to the large antennapedia genes, whose genes can be over 100kb in length. The collection of these products is referred to as heterogeneous nuclear rna (hnRNA) Bi pre- mRNAs These hnrNa are processed to e mRNAs called pre-mRNAS
一、hnRNA Eucaryotic RNA Pol II transcribes a variety of different genes, from snRNA genes of 60-300nt to the large Antennapedia genes, whose genes can be over 100kb in length. The collection of these products is referred to as heterogeneous nuclear RNA (hnRNA) . 二、pre-mRNAs These hnRNA are processed to give mRNAs called pre-mRNAs
hnrnp: hetrogenenous nuclear ribonucleoprotein The hnrNa is rapidly covered in proteins to form hnrnp The proteins involved have been classified as hnrNa proteins A-U These proteins are organized as a tetramer. Three copies of tetramer are combined with a RNa molecule of 600-700nt, called hnrNP particles, each particle has a size of 30-40S
三、hnRNP : hetrogenenous nuclear ribonucleoprotein The hnRNA is rapidly covered in proteins to form hnRNP. The proteins involved have been classified as hnRNA proteins A-U. These proteins are organized as a tetramer. Three copies of tetramer are combined with a RNA molecule of 600-700nt , called hnRNP particles, each particle has a size of 30-40S
The hnrnp protein are thought to help keep the hnrna in a single-stranded form and assist in the various RNa processing reactions
The hnRNP protein are thought to help keep the hnRNA in a single-stranded form and assist in the various RNA processing reactions
四 、 snrNP Particles snRNAs transcribed by rna pol ll complex with specific protein to form SnRNP. These rna are rich in uracil and are denoted as U1、U2etc U1、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 hey 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( tron 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
5-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 giving 5-5 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 在帽1中可被甲基化>H2 位置 CH 帽1位置XOCH3 O-P-O-CH 帽2位置CH O-P-0 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