fttp://moleco.sjtu.edu.cn/uploads/course/分子生
物学（许老师）
第三节 mRNA Processing,hnRNPs and snRNPs
一,hnRNA
二,pre-mRNAs
三,hnRNP
四,snRNPs
五,pre-mRNA processing
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.
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.
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 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 。
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 NH
2
位 置
C N
O C H
3
N C
C H
C N H C C
H N C N N
C H
O C O O O
2
HN
N
N
C H
2
O P O P O P O C H
O O O
帽 1 位 置 O CH
3
O
O P O C H
2
O
帽 2 位 置 O CH
3
O
O P O
O
图 1 3 - m R N A 5 ’ 端的帽子位置和可被甲基化的位点
转录起始
e l o n g a t i o n
5 ’ c a p A A U A A A
s p l i c i n g
P o l y ( A ) p o l y m e r a s e
5 ’ c a p A A U A A A A n
图 1 3 - m R N A 3 ’ a d d i t i o n g o f P o l y ( A ) t a i l
2 3’-tailing, 3’-cleavage and polyadenylation
(1) Polyadenylation signal:
5’ Cap…..…..AAUAA..(20bases).CA………UUGUGUUG
signal Poly(A) GUrich region
cleavage site addition site
? (1) CPSF recognizes AAUAAA and binds
to it;
? (2) Cf cleavages at the specific point of 11
－ 30 nt downstream AAUAAA;
? (3) poly(A) polymerase [末端腺苷转移酶 ]
adds A to form poly(A);
? (4) poly(A) is combined with PBP.
(2) The procedures of PolyA formation
The poly(A) tail is thought to help stabilize
the molecule since a protein binds to it to
resist 3’ exonuclease action and may help in
the translation in the cytoplasm.
This feature has allowed the purification of
mRNA,for cDNA library construction.
(3) The function of polyA
3 splicing
During the processing,some sequences
are cut out from the central regions and
the outer portions joined,These
intervening sequences,or introns,
interrupt those sequence that will
become adjacent regions of mature
mRNA,the exons which are usually the
protein-coding regions of mRNA.
5’ 3’
intron
5’
Pre-mRNA
Mature mRNA
exton
(1) It takes place in the nucleus,before the
mature mRNA can be exported to the
cytoplasm.
Features of pre-mRNA splicing:
(2) It requires a set of specific sequences:
5’..AAGUAAGU ……,CURAY..(10-40)…(U/C) 11NCAG G…,3’
Intron
exonexon
R:Purine Y:pyrimidine
Branchpoint sequence Polyprimidine
(3) It takes places in a two-step
reaction,snRNPs are involved.
GU
U1 AGU5
A
U2
2 ’
0 H
5 ’ 外显子 1 G U Py N CU Pu A P y A G 外显子 2 3 ’
5 ’ 外显子 1 G 外显子 2
O H 3 ’ U A G 3 ’
T A Py
套索结构
5 ’ 外显子 1 外显子 2 3 ’
图 1 3 - Ⅱ 类内含子 剪接的模式
(4) The final step is methylation on the N6
position of A residues particularly in the
the sequence 5’-RRACX-3’.
第四节 Alternative mRNA processing
The alternative mRNA processing is the
conversion of pre-mRNA species into
more than one type of mature mRNA.
一,Alternative selection of poly(A) sites
The transcript is polyadenylated at different
locations
1 2
3
4 5 6
AATAA AATAA
1 2
3
4
4 5 6321
Calcitonin (thyoid cell 甲状腺 )
CGRP ( brain )
Immunoglobulin heavy chain:
Per-mRNA
polyA2 polyA1
Membrane-anchor
protein in virgin cell
Secreted form in plasma
二,Alternative selection of promoters
P1 P2 ?-amylase in salivary gland
(Stronger splicing)
?-amylase in liver
(weaker splicing)
三,Alternative selection of intron or exon
P element transposable sysytem in Drosophila
P element
In somatic cell
In germline cell
repressor
transposase
四,RNA editing
(1) Definition
The sequence of the primary transcript is
altered by either changing,inserting or
deleting residues at the specific points
along the molecules is called RNA editing,
They seem to be more common in nonvertebrates.
In human,the unedited mRNA of apolipoprotein
(载脂蛋白 ) B makes correct size of protein in the
liver,
Editing causes a single base change from C to U in
the Apo-B pre-mRNA,creating a stop codon in the
mRNA at position 6666,resulting a truncated
protein in intestinal cells,
(2) Samples
A p o B 基因有 29 个外显子
C A A 第 2153 个密码子编码 G l u
编辑
C A A U A A
翻译 翻译
在肝中剪接后的 m RN A 肠中的 m RN A 经编辑
编码了 4 5 6 3 a a 的载脂蛋白 产生了终止密码子，在
2 1 5 3 a a 处终止合成
图 1 3 - 4 2 载脂蛋白的基因 A p o B 在肠中经过编辑，
引入终止密码子，不能翻译成完整的载脂蛋白。
( 参考 B, L e w i n,, G E N E S,Ⅵ,1 9 9 7, F i g 3 1, 1 4 )
coxII gene editing in T.brucei
T
U A U A U G U U U U G UU G U U U A UU A U G U GA UU A U GG U U U U G U U U U U U A UU G G U A U U U U U U A U A UUU A
UUU AA U U U G UU GA U A A A U A C A U U U U A U U U G UU UG UU AA U U U U U U U G U U U U G U G U U U U U G G UU
TT TTTT
U A G G U U U U U U U G UU G U U G UU G U U U U G U A UU A U GA UU G A G UUU G UU G U U U GG U U U U U U G U U U U
TT TTTT
UU G U G A A A C C A G UU A U G A G A G U U U G C A UU G UU A UUU A UU ACA UU A A G UU G G U G U U U U U GG UU C
图 1 3 -4 4 锥虫 ( T, b r u c e i ) c o x Ⅱ 基因的部分 R N A 顺序。很多 U( 红色 ) 在 DNA 中未编码，而另一些在
D N A 中编码的 T( 紫色 ) 在 m R N A 中被删除了。 ( 参考 B, L e w i n,, G E N E S, Ⅵ,1 9 9 7, F i g 3 1, 1 6 )
(3) The biological significance of editing:
? proofreading ；
?translation regulation；
?expanded genetic information.
(4),Mechanics of editing
?In1990,the guide RNA was found by L,
Simpsom et al.,
3 ’
5 ’
’
3 ’
5 ’ P 3 ’
U - O H
U
U
U
U
5 ’ O H
U
U
U
U
U
U
U - O H
U
U
U
图 1 3 - 编辑的转酯模型
第一次转移
第二次转移
物学（许老师）
第三节 mRNA Processing,hnRNPs and snRNPs
一,hnRNA
二,pre-mRNAs
三,hnRNP
四,snRNPs
五,pre-mRNA processing
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.
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.
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 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 。
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 NH
2
位 置
C N
O C H
3
N C
C H
C N H C C
H N C N N
C H
O C O O O
2
HN
N
N
C H
2
O P O P O P O C H
O O O
帽 1 位 置 O CH
3
O
O P O C H
2
O
帽 2 位 置 O CH
3
O
O P O
O
图 1 3 - m R N A 5 ’ 端的帽子位置和可被甲基化的位点
转录起始
e l o n g a t i o n
5 ’ c a p A A U A A A
s p l i c i n g
P o l y ( A ) p o l y m e r a s e
5 ’ c a p A A U A A A A n
图 1 3 - m R N A 3 ’ a d d i t i o n g o f P o l y ( A ) t a i l
2 3’-tailing, 3’-cleavage and polyadenylation
(1) Polyadenylation signal:
5’ Cap…..…..AAUAA..(20bases).CA………UUGUGUUG
signal Poly(A) GUrich region
cleavage site addition site
? (1) CPSF recognizes AAUAAA and binds
to it;
? (2) Cf cleavages at the specific point of 11
－ 30 nt downstream AAUAAA;
? (3) poly(A) polymerase [末端腺苷转移酶 ]
adds A to form poly(A);
? (4) poly(A) is combined with PBP.
(2) The procedures of PolyA formation
The poly(A) tail is thought to help stabilize
the molecule since a protein binds to it to
resist 3’ exonuclease action and may help in
the translation in the cytoplasm.
This feature has allowed the purification of
mRNA,for cDNA library construction.
(3) The function of polyA
3 splicing
During the processing,some sequences
are cut out from the central regions and
the outer portions joined,These
intervening sequences,or introns,
interrupt those sequence that will
become adjacent regions of mature
mRNA,the exons which are usually the
protein-coding regions of mRNA.
5’ 3’
intron
5’
Pre-mRNA
Mature mRNA
exton
(1) It takes place in the nucleus,before the
mature mRNA can be exported to the
cytoplasm.
Features of pre-mRNA splicing:
(2) It requires a set of specific sequences:
5’..AAGUAAGU ……,CURAY..(10-40)…(U/C) 11NCAG G…,3’
Intron
exonexon
R:Purine Y:pyrimidine
Branchpoint sequence Polyprimidine
(3) It takes places in a two-step
reaction,snRNPs are involved.
GU
U1 AGU5
A
U2
2 ’
0 H
5 ’ 外显子 1 G U Py N CU Pu A P y A G 外显子 2 3 ’
5 ’ 外显子 1 G 外显子 2
O H 3 ’ U A G 3 ’
T A Py
套索结构
5 ’ 外显子 1 外显子 2 3 ’
图 1 3 - Ⅱ 类内含子 剪接的模式
(4) The final step is methylation on the N6
position of A residues particularly in the
the sequence 5’-RRACX-3’.
第四节 Alternative mRNA processing
The alternative mRNA processing is the
conversion of pre-mRNA species into
more than one type of mature mRNA.
一,Alternative selection of poly(A) sites
The transcript is polyadenylated at different
locations
1 2
3
4 5 6
AATAA AATAA
1 2
3
4
4 5 6321
Calcitonin (thyoid cell 甲状腺 )
CGRP ( brain )
Immunoglobulin heavy chain:
Per-mRNA
polyA2 polyA1
Membrane-anchor
protein in virgin cell
Secreted form in plasma
二,Alternative selection of promoters
P1 P2 ?-amylase in salivary gland
(Stronger splicing)
?-amylase in liver
(weaker splicing)
三,Alternative selection of intron or exon
P element transposable sysytem in Drosophila
P element
In somatic cell
In germline cell
repressor
transposase
四,RNA editing
(1) Definition
The sequence of the primary transcript is
altered by either changing,inserting or
deleting residues at the specific points
along the molecules is called RNA editing,
They seem to be more common in nonvertebrates.
In human,the unedited mRNA of apolipoprotein
(载脂蛋白 ) B makes correct size of protein in the
liver,
Editing causes a single base change from C to U in
the Apo-B pre-mRNA,creating a stop codon in the
mRNA at position 6666,resulting a truncated
protein in intestinal cells,
(2) Samples
A p o B 基因有 29 个外显子
C A A 第 2153 个密码子编码 G l u
编辑
C A A U A A
翻译 翻译
在肝中剪接后的 m RN A 肠中的 m RN A 经编辑
编码了 4 5 6 3 a a 的载脂蛋白 产生了终止密码子，在
2 1 5 3 a a 处终止合成
图 1 3 - 4 2 载脂蛋白的基因 A p o B 在肠中经过编辑，
引入终止密码子，不能翻译成完整的载脂蛋白。
( 参考 B, L e w i n,, G E N E S,Ⅵ,1 9 9 7, F i g 3 1, 1 4 )
coxII gene editing in T.brucei
T
U A U A U G U U U U G UU G U U U A UU A U G U GA UU A U GG U U U U G U U U U U U A UU G G U A U U U U U U A U A UUU A
UUU AA U U U G UU GA U A A A U A C A U U U U A U U U G UU UG UU AA U U U U U U U G U U U U G U G U U U U U G G UU
TT TTTT
U A G G U U U U U U U G UU G U U G UU G U U U U G U A UU A U GA UU G A G UUU G UU G U U U GG U U U U U U G U U U U
TT TTTT
UU G U G A A A C C A G UU A U G A G A G U U U G C A UU G UU A UUU A UU ACA UU A A G UU G G U G U U U U U GG UU C
图 1 3 -4 4 锥虫 ( T, b r u c e i ) c o x Ⅱ 基因的部分 R N A 顺序。很多 U( 红色 ) 在 DNA 中未编码，而另一些在
D N A 中编码的 T( 紫色 ) 在 m R N A 中被删除了。 ( 参考 B, L e w i n,, G E N E S, Ⅵ,1 9 9 7, F i g 3 1, 1 6 )
(3) The biological significance of editing:
? proofreading ；
?translation regulation；
?expanded genetic information.
(4),Mechanics of editing
?In1990,the guide RNA was found by L,
Simpsom et al.,
3 ’
5 ’
’
3 ’
5 ’ P 3 ’
U - O H
U
U
U
U
5 ’ O H
U
U
U
U
U
U
U - O H
U
U
U
图 1 3 - 编辑的转酯模型
第一次转移
第二次转移
