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Specific combinations of SR proteins associate with single pre-messenger RNAs in vivo and contribute different functions.

Björk P, Jin S, Zhao J, Singh OP, Persson JO, Hellman U, Wieslander L - J. Cell Biol. (2009)

Bottom Line: However, hrp45/SRp55 is distributed differently in the pre-mRNPs along the gene compared with ASF/SF2, SC35, and 9G8, suggesting functional differences.All four SR proteins are associated with the BR mRNPs during export to the cytoplasm.ASF/SF2 is associated with polyribosomes, whereas SC35, 9G8, and hrp45/SRp55 cosediment with monoribosomes.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular Biology and Functional Genomics, Stockholm University, SE-106 91 Stockholm, Sweden.

ABSTRACT
Serine/arginine-rich (SR) proteins are required for messenger RNA (mRNA) processing, export, surveillance, and translation. We show that in Chironomus tentans, nascent transcripts associate with multiple types of SR proteins in specific combinations. Alternative splicing factor (ASF)/SF2, SC35, 9G8, and hrp45/SRp55 are all present in Balbiani ring (BR) pre-messenger ribonucleoproteins (mRNPs) preferentially when introns appear in the pre-mRNA and when cotranscriptional splicing takes place. However, hrp45/SRp55 is distributed differently in the pre-mRNPs along the gene compared with ASF/SF2, SC35, and 9G8, suggesting functional differences. All four SR proteins are associated with the BR mRNPs during export to the cytoplasm. Interference with SC35 indicates that SC35 is important for the coordination of splicing, transcription, and 3' end processing and also for nucleocytoplasmic export. ASF/SF2 is associated with polyribosomes, whereas SC35, 9G8, and hrp45/SRp55 cosediment with monoribosomes. Thus, individual endogenous pre-mRNPs/mRNPs bind multiple types of SR proteins during transcription, and these SR proteins accompany the mRNA and play different roles during the gene expression pathway in vivo.

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The SR proteins are differently distributed along active BR genes. Chromosome IV was stained with anti-SC35, anti-9G8, anti-ASF/SF2, or anti-hrp45/SRp55 antibodies and analyzed by EM. For each SR protein, all gold particles were attributed to proximal (p), middle (m), or distal (d) segments of the BR gene (Table I). (A) A section through a BR gene locus stained with anti-hrp45/SRp55 antibody is shown to illustrate proximal, middle, and distal gene segments. (B) An active BR gene with growing BR pre-mRNPs is shown schematically based on EM reconstruction data (Daneholt et al., 1982). The three segments (p, m, and d) of the active gene are indicated. Each segment is characterized by the morphology of the BR pre-mRNPs. Bar, 200 nm.
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fig4: The SR proteins are differently distributed along active BR genes. Chromosome IV was stained with anti-SC35, anti-9G8, anti-ASF/SF2, or anti-hrp45/SRp55 antibodies and analyzed by EM. For each SR protein, all gold particles were attributed to proximal (p), middle (m), or distal (d) segments of the BR gene (Table I). (A) A section through a BR gene locus stained with anti-hrp45/SRp55 antibody is shown to illustrate proximal, middle, and distal gene segments. (B) An active BR gene with growing BR pre-mRNPs is shown schematically based on EM reconstruction data (Daneholt et al., 1982). The three segments (p, m, and d) of the active gene are indicated. Each segment is characterized by the morphology of the BR pre-mRNPs. Bar, 200 nm.

Mentions: The immunofluorescence results, including sensitivity to RNase, suggested that each individual transcript binds multiple SR proteins. The association of the SR proteins with BR1 and BR2 pre-mRNPs was further investigated by immuno-EM. The BR1 and BR2 pre-mRNAs associate with various RNA-binding proteins cotranscriptionally and gradually form morphologically characteristic pre-mRNA–protein complexes (Daneholt, 2001), which are referred to as BR pre-mRNPs (see Fig. 4 B). We found that the SR proteins were associated with BR pre-mRNPs at all stages of transcription and packaging. Growing BR pre-mRNPs labeled for each SR protein are shown in Fig. 3 (A–D).


Specific combinations of SR proteins associate with single pre-messenger RNAs in vivo and contribute different functions.

Björk P, Jin S, Zhao J, Singh OP, Persson JO, Hellman U, Wieslander L - J. Cell Biol. (2009)

The SR proteins are differently distributed along active BR genes. Chromosome IV was stained with anti-SC35, anti-9G8, anti-ASF/SF2, or anti-hrp45/SRp55 antibodies and analyzed by EM. For each SR protein, all gold particles were attributed to proximal (p), middle (m), or distal (d) segments of the BR gene (Table I). (A) A section through a BR gene locus stained with anti-hrp45/SRp55 antibody is shown to illustrate proximal, middle, and distal gene segments. (B) An active BR gene with growing BR pre-mRNPs is shown schematically based on EM reconstruction data (Daneholt et al., 1982). The three segments (p, m, and d) of the active gene are indicated. Each segment is characterized by the morphology of the BR pre-mRNPs. Bar, 200 nm.
© Copyright Policy - openaccess
Related In: Results  -  Collection

License 1 - License 2
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getmorefigures.php?uid=PMC2654125&req=5

fig4: The SR proteins are differently distributed along active BR genes. Chromosome IV was stained with anti-SC35, anti-9G8, anti-ASF/SF2, or anti-hrp45/SRp55 antibodies and analyzed by EM. For each SR protein, all gold particles were attributed to proximal (p), middle (m), or distal (d) segments of the BR gene (Table I). (A) A section through a BR gene locus stained with anti-hrp45/SRp55 antibody is shown to illustrate proximal, middle, and distal gene segments. (B) An active BR gene with growing BR pre-mRNPs is shown schematically based on EM reconstruction data (Daneholt et al., 1982). The three segments (p, m, and d) of the active gene are indicated. Each segment is characterized by the morphology of the BR pre-mRNPs. Bar, 200 nm.
Mentions: The immunofluorescence results, including sensitivity to RNase, suggested that each individual transcript binds multiple SR proteins. The association of the SR proteins with BR1 and BR2 pre-mRNPs was further investigated by immuno-EM. The BR1 and BR2 pre-mRNAs associate with various RNA-binding proteins cotranscriptionally and gradually form morphologically characteristic pre-mRNA–protein complexes (Daneholt, 2001), which are referred to as BR pre-mRNPs (see Fig. 4 B). We found that the SR proteins were associated with BR pre-mRNPs at all stages of transcription and packaging. Growing BR pre-mRNPs labeled for each SR protein are shown in Fig. 3 (A–D).

Bottom Line: However, hrp45/SRp55 is distributed differently in the pre-mRNPs along the gene compared with ASF/SF2, SC35, and 9G8, suggesting functional differences.All four SR proteins are associated with the BR mRNPs during export to the cytoplasm.ASF/SF2 is associated with polyribosomes, whereas SC35, 9G8, and hrp45/SRp55 cosediment with monoribosomes.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular Biology and Functional Genomics, Stockholm University, SE-106 91 Stockholm, Sweden.

ABSTRACT
Serine/arginine-rich (SR) proteins are required for messenger RNA (mRNA) processing, export, surveillance, and translation. We show that in Chironomus tentans, nascent transcripts associate with multiple types of SR proteins in specific combinations. Alternative splicing factor (ASF)/SF2, SC35, 9G8, and hrp45/SRp55 are all present in Balbiani ring (BR) pre-messenger ribonucleoproteins (mRNPs) preferentially when introns appear in the pre-mRNA and when cotranscriptional splicing takes place. However, hrp45/SRp55 is distributed differently in the pre-mRNPs along the gene compared with ASF/SF2, SC35, and 9G8, suggesting functional differences. All four SR proteins are associated with the BR mRNPs during export to the cytoplasm. Interference with SC35 indicates that SC35 is important for the coordination of splicing, transcription, and 3' end processing and also for nucleocytoplasmic export. ASF/SF2 is associated with polyribosomes, whereas SC35, 9G8, and hrp45/SRp55 cosediment with monoribosomes. Thus, individual endogenous pre-mRNPs/mRNPs bind multiple types of SR proteins during transcription, and these SR proteins accompany the mRNA and play different roles during the gene expression pathway in vivo.

Show MeSH