Sandbox ceg1p Steven Paris

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== Function of Ceg1p and the Cet1-Ceg1 mRNA Capping Complex ==
== Function of Ceg1p and the Cet1-Ceg1 mRNA Capping Complex ==
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Ceg1p is an mRNA guanylyltransferase in ''Saccharomyces cerevisiae'' that forms a heterotetramer with the RNA triphosphatase Cet1p which is called the mRNA capping apparatus. This complex is recruited by RNA polymerase II (RNAP-II) and performs the first two steps in the 5’-guanisine mRNA capping mechanism. Cet1p hydrolyzes a phosphate from the 5’-triphosphate end of the pre-mRNA.<ref name="source one">PMID:20159466</ref> The Ceg1p guanylyltransferase then adds a guanosine monophosphate to the 5' end of the pre-mRNA, creating a 5'-5' triphosphate linkage. In the final step, an RNA methyltransferase comes and adds a methyl group to the N7 atom of the guanine, completing the 5'-guanine cap.<ref name="source two">PMID:24172134</ref> This 5’ capping is necessary for cells to live in yeast among other organisms. The interactions between Cet1p and Ceg1p are extremely important for inducing capping activity. These interactions both stimulate Ceg1p GMP transfer and help localize the complex in the nucleus where RNAP-II can recruit it.<ref name="source three">PMID:24205062</ref> The capping apparatus is specifically recruited to the Rpb1p subunit of RNAP-II. It binds to the serine-5-phosphorylated-carboxy terminal domain (CTD) of Rpb1p. The capping mechanism occurs while transcription is still occurring, beginning when around 20-25 nucleotides are successfully transcribed by RNAP-II.<ref name="source two"/> Another role that the Cet1-Ceg1 complex has is the suppression of RNAP-II transcription. This transcriptional control involves the capping complex keeping RNAP-II from reinitiating transcription.<ref>PMID:12419231</ref> The capping complex has also been suggested to have regulatory roles in other cellular functions such as cell proliferation and RNA interference.<ref name="source two"/>
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Ceg1p is an mRNA guanylyltransferase in ''Saccharomyces cerevisiae'' that forms a heterotetramer with the RNA triphosphatase Cet1p, which is called the mRNA capping apparatus. This complex is recruited by RNA polymerase II (RNAP-II) and performs the first two steps in the 5’-guanisine mRNA capping mechanism. Cet1p hydrolyzes a phosphate from the 5’-triphosphate end of the pre-mRNA.<ref name="source one">PMID:20159466</ref> The Ceg1p guanylyltransferase then adds a guanosine monophosphate to the 5' end of the pre-mRNA, creating a 5'-5' triphosphate linkage. In the final step, an RNA methyltransferase comes and adds a methyl group to the N7 atom of the guanine, completing the 5'-guanine cap.<ref name="source two">PMID:24172134</ref> This 5’ capping is necessary for cells to live in yeast among other organisms. The interactions between Cet1p and Ceg1p are extremely important for inducing capping activity. These interactions both stimulate Ceg1p GMP transfer and help localize the complex in the nucleus where RNAP-II can recruit it.<ref name="source three">PMID:24205062</ref> The capping apparatus is specifically recruited to the Rpb1p subunit of RNAP-II. It binds to the serine-5-phosphorylated-carboxy terminal domain (CTD) of Rpb1p. The capping mechanism occurs alongside transcription, beginning when around 20-25 nucleotides are successfully transcribed by RNAP-II.<ref name="source two"/> Another role that the Cet1-Ceg1 complex has is the suppression of RNAP-II transcription. This transcriptional control involves the capping complex keeping RNAP-II from reinitiating transcription.<ref>PMID:12419231</ref> The capping complex has also been suggested to have regulatory roles in other cellular functions such as cell proliferation and RNA interference.<ref name="source two"/>
== Structure of Ceg1p and Interactions with Cet1p in the Capping Apparatus ==
== Structure of Ceg1p and Interactions with Cet1p in the Capping Apparatus ==
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The <scene name='60/602708/Cet1-ceg1_capping_apparatus/2'>Cet1p-Ceg1p capping apparatus</scene> is composed of a <scene name='60/602708/Cet1p_homodimer/1'>Cet1p Homodimer</scene> and two <scene name='60/602708/Ceg1p_monomers/1'>Ceg1p Monomers</scene>, one on each end of the homodimer. The capping apparatus may also have only one Ceg1p monomer attached, forming a heterotrimer complex. A <scene name='60/602708/Ceg1p_single_w_domains/1'>Ceg1p monomer</scene> contains two major domains: a nucleotydil transferase (NT) domain and an oligonucleotide binding (OB) domain. The OB domain interacts with Cet1p, while the NT domain interacts with RNAP-II. For the Cet1p, only amino acids 241-549 of each monomer are required for the complex to properly cap mRNA.<ref name="source one"/> The Ceg1p monomers interact with the Cet1p homodimer though the <scene name='60/602708/Ceg_cet_interaction/1'>WAQKW motif</scene> of Cet1p. The motif is followed by a flexible linker.<ref name="source one"/><ref name="source five">PMID:10572165</ref> The motif extends from the Cet1p monomer furthest from Ceg1p and binds it to the homodimer. This interaction allows the Ceg1p to maintain a conformation that allows it to bind to both the Cet1p homodimer, and RNAP-II during the capping process. The OB and NT domains open and close so that GMP can be properly transferred to the 5' end of the mRNA. Many components of the Cet1-Ceg1 capping apparatus are conserved across evolution. Some highly conserved components include: the NT and OB domains of Ceg1p, the WAQKW motif of Cet1p and the capping apparatus recruitment by RNAP-II.<ref name="source one"/> In ''Candida albicans'', the guanylyltransferase-binding domain was conserved from ''S. cerevisiae''.<ref name="source five"/> This is only one example of the high conservation observed for the Cet1-Ceg1 capping apparatus.
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The <scene name='60/602708/Cet1-ceg1_capping_apparatus/2'>Cet1p-Ceg1p capping apparatus</scene> is composed of a <scene name='60/602708/Cet1p_homodimer/1'>Cet1p Homodimer</scene> and two <scene name='60/602708/Ceg1p_monomers/1'>Ceg1p Monomers</scene>, one on each end of the homodimer. The capping apparatus may also have only one Ceg1p monomer attached, forming a heterotrimer complex. A <scene name='60/602708/Ceg1p_single_w_domains/1'>Ceg1p monomer</scene> contains two major domains: a nucleotydil transferase (NT) domain and an oligonucleotide binding (OB) domain. The OB domain interacts with Cet1p, while the NT domain interacts with RNAP-II. For the Cet1p, only amino acids 241-549 of each monomer are required for the complex to properly cap the pre-mRNA.<ref name="source one"/> The Ceg1p monomers interact with the Cet1p homodimer though the <scene name='60/602708/Ceg_cet_interaction/1'>WAQKW motif</scene> of Cet1p. This motif is followed by a flexible linker.<ref name="source one"/><ref name="source five">PMID:10572165</ref> The motif extends from the Cet1p monomer furthest from Ceg1p and binds it to the homodimer. This interaction allows the Ceg1p to maintain a conformation that allows it to bind to both the Cet1p homodimer, and RNAP-II during the capping process. The OB and NT domains open and close so that GMP can be properly transferred to the 5' end of the pre-mRNA. Many components of the Cet1-Ceg1 capping apparatus are conserved across evolution. Some highly conserved components include: the NT and OB domains of Ceg1p, the WAQKW motif of Cet1p and the capping apparatus recruitment by RNAP-II.<ref name="source one"/> In ''Candida albicans'', the guanylyltransferase-binding domain was conserved from ''S. cerevisiae''.<ref name="source five"/> This is only one example of the high conservation observed for the Cet1-Ceg1 capping apparatus.
== Cet1-Ceg1 Interaction with RNAP-II ==
== Cet1-Ceg1 Interaction with RNAP-II ==
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When 22-25 nucleotides have been transcribed by RNAP-II, the Cet1-Ceg1 apparatus is recruited to the Rpb1p subunit's CTD to perform 5' capping on the pre-mRNA.<ref name="source two"/> Ceg1p comes in direct contact with the CTD so that 5' capping can occur. This interaction with the CTD occurs in the NT domain of Ceg1p. This interaction is highly conserved across both yeast and mammals.<ref name="source one"/><ref name="source three"/> Cet1p, while still in complex with Ceg1p, Cet1p does not directly directly bind to RNAP-II.<ref name="source six">Takase Y., Takagi T., Komarnitsky P. B., Buratowski S., 2000. The essential interaction between yeast mRNA capping enzyme subunits is not required for triphosphatase function in vivo. Mol. Cell. Biol. 20: 9307–9316. PMID:11094081 '''[http://dx.doi.org/10.1128/MCB.20.24.9307-9316.2000''' DOI:10.1128/MCB.20.24.9307-9316.2000''']'''</ref> When Ceg1p binds to the CTD, it gains an unfavorable conformation that doesn't allow 5' capping to occur. It is the combination of Cet1p's flexible linker and the general flexibility of the CTD that allow for Ceg1p to transfer the GMP cap to the pre-mRNA. This flexibility on both sides of the Ceg1p monomer allow both the NT and OB domains to open and close into the conformations needed the GMP transfer mechanism.<ref name="source one"/><ref name="source six"/> The dissociation between the Cet1-Ceg1 is unknown, but is thought to occur after elongation occurs.<ref name="source one"/>
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When 20-25 nucleotides have been transcribed by RNAP-II, the Cet1-Ceg1 apparatus is recruited to the Rpb1p subunit's CTD to perform 5' capping on the pre-mRNA.<ref name="source two"/> Ceg1p comes in direct contact with the CTD so that 5' capping can occur. The interaction with the CTD occurs in the NT domain of Ceg1p. This interaction is highly conserved across both yeast and mammals.<ref name="source one"/><ref name="source three"/> Cet1p, while still in complex with Ceg1p, does not directly directly bind to RNAP-II.<ref name="source six">Takase Y., Takagi T., Komarnitsky P. B., Buratowski S., 2000. The essential interaction between yeast mRNA capping enzyme subunits is not required for triphosphatase function in vivo. Mol. Cell. Biol. 20: 9307–9316. PMID:11094081 '''[http://dx.doi.org/10.1128/MCB.20.24.9307-9316.2000''' DOI:10.1128/MCB.20.24.9307-9316.2000''']'''</ref> When Ceg1p binds to the CTD, it gains an unfavorable conformation that doesn't allow 5' capping to occur. It is the combination of Cet1p's flexible linker and the general flexibility of the CTD that allow for Ceg1p to transfer the GMP cap to the pre-mRNA. This flexibility on both sides of the Ceg1p monomer allow both the NT and OB domains of Ceg1p to open and close into the conformations needed for GMP transfer.<ref name="source one"/><ref name="source six"/> The dissociation between the Cet1-Ceg1 complex and RNAP-II is unknown, but is thought to occur after elongation occurs.<ref name="source one"/>
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== About This Structure ==
== About This Structure ==
[http://proteopedia.org/wiki/index.php/3kyh 3kyh] is a 4 chain structure with sequence from [http://en.wikipedia.org/wiki/Saccharomyces_cerevisiae ''Saccharomyces cerevisiae'']. Full crystallographic information is available from [http://oca.weizmann.ac.il/oca-bin/ocashort?id=3KYH OCA].
[http://proteopedia.org/wiki/index.php/3kyh 3kyh] is a 4 chain structure with sequence from [http://en.wikipedia.org/wiki/Saccharomyces_cerevisiae ''Saccharomyces cerevisiae'']. Full crystallographic information is available from [http://oca.weizmann.ac.il/oca-bin/ocashort?id=3KYH OCA].

Current revision

Ceg1p mRNA Guanylyltransferase

Cet1-Ceg1 mRNA Capping Apparatus [3kyh]

Drag the structure with the mouse to rotate

References

  1. ↑ 1.0 1.1 1.2 1.3 1.4 1.5 1.6 Gu M, Rajashankar KR, Lima CD. Structure of the Saccharomyces cerevisiae Cet1-Ceg1 mRNA capping apparatus. Structure. 2010 Feb 10;18(2):216-27. PMID:20159466 doi:10.1016/j.str.2009.12.009
  2. ↑ 2.0 2.1 2.2 2.3 Lahudkar S, Durairaj G, Uprety B, Bhaumik SR. A novel role for Cet1p mRNA 5'-triphosphatase in promoter proximal accumulation of RNA polymerase II in Saccharomyces cerevisiase. Genetics. 2014 Jan;196(1):161-76. doi: 10.1534/genetics.113.158535. Epub 2013 Oct, 30. PMID:24172134 doi:http://dx.doi.org/10.1534/genetics.113.158535
  3. ↑ 3.0 3.1 Takizawa N, Fujiwara T, Yamasaki M, Saito A, Fukao A, Nomoto A, Mizumoto K. The essential role for the RNA triphosphatase Cet1p in nuclear import of the mRNA capping enzyme Cet1p-Ceg1p complex of Saccharomyces cerevisiae. PLoS One. 2013 Oct 30;8(10):e78000. doi: 10.1371/journal.pone.0078000., eCollection 2013. PMID:24205062 doi:http://dx.doi.org/10.1371/journal.pone.0078000
  4. ↑ Myers LC, Lacomis L, Erdjument-Bromage H, Tempst P. The yeast capping enzyme represses RNA polymerase II transcription. Mol Cell. 2002 Oct;10(4):883-94. PMID:12419231
  5. ↑ 5.0 5.1 Ho CK, Lehman K, Shuman S. An essential surface motif (WAQKW) of yeast RNA triphosphatase mediates formation of the mRNA capping enzyme complex with RNA guanylyltransferase. Nucleic Acids Res. 1999 Dec 15;27(24):4671-8. PMID:10572165
  6. ↑ 6.0 6.1 Takase Y., Takagi T., Komarnitsky P. B., Buratowski S., 2000. The essential interaction between yeast mRNA capping enzyme subunits is not required for triphosphatase function in vivo. Mol. Cell. Biol. 20: 9307–9316. PMID:11094081 DOI:10.1128/MCB.20.24.9307-9316.2000
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