“SR proteins and related factors play widespread roles in alternative pre-mRNA s
ID: 205249 • Letter: #
Question
“SR proteins and related factors play widespread roles in alternative pre-mRNA splicing and are known to promote splice site recognition through their Arg–Ser-rich effector domains. However, binding of SR regulators to some targets results in repression of splice sites through a distinct mechanism. Here, we investigate how activated and repressed targets of the Drosophila SR regulator Transformer2 elicit its differing effects on splicing. We find that, like activation, repression affects early steps in the recognition of splice sites and spliceosome assembly. Repositioning of regulatory elements reveals that Tra2 complexes that normally repress splicing from intronic positions activate splicing when located in an exon. Protein tethering experiments demonstrate that this position dependence is an intrinsic property of Tra2 and further show that repression and activation are mediated by separate effector domains of this protein. When other Drosophila SR factors (SF2 and Rbp1) that activate splicing from exonic positions were tethered intronically they failed to either activate or repress splicing. Interestingly, both activities of Tra2 favor the exonic identity of the RNA sequences that encompass its binding sites. This suggests a model in which these two opposite functions act in concert to define both the position and extent of alternatively spliced exons.” NAR 40: 428.
(4 points) What SR-related regulators control the splicing of dsx and fru pre-mRNAs?
(4 points) How are other SR factors and ESEs involved in alternative splicing of dsx and fru?
(4 points) How is it possible for Tra2 to repress splicing of some targets?
(4 points) Which data suggests the activator and repressor activities of Tra2 are dependent on different effector sequences?
(4 points) Is it possible for the activation and repression properties to work side by side to ensure the accuracy of the exon? If so, please explain.
https://www.ncbi.nlm.nih.gov/pubmed/21914724
Explanation / Answer
4 points) What SR-related regulators control the splicing of dsx and fru pre-mRNAs?
Ans: SR-related regulators control the splicing of dsx and fru pre-mRNAs are Transformer (Tra) and Transformer-2(Tra-2).
(4 points) How are other SR factors and ESEs involved in alternative splicing of dsx and fru?
Ans:Transformer (Tra) and Transformer-2(Tra-2) and other SR proteins, combines with the exonic splicing enhancers (ESEs) to operate the splicing process. This enhancer complex binds with the dsx and fru pre-mRNAs and thus promoting the use of sex-specific alternative splice sites. SR factors contains characteristic an Arg–Ser-rich effector regions. This effector domain directly binds to the pre-spliceosomal complexes to help their assembly at the affected splice sites.
(4 points) How is it possible for Tra2 to repress splicing of some targets?
Ans:Due to presence of the negative feedback mechanism Tra2 protein is responsible for the retention of the M1 intrinic region within the pre-RNA of Tra2 this causes the limited functioning opportunities for Tra2 protein. An intronic splicing silencer (ISS) region is located with the multiple Tra2-binding sites in the pre-RNA. This ISS region is responsible for the repression. The repression of M1 intrinic region and the activation of dsx splicing with the help of Tra2 occurred simultaneously in the same cell.
(4 points) Which data suggests the activator and repressor activities of Tra2 are dependent on different effector sequences?
Ans:A fusion protein having carboxy-terminal Arg–Ser-rich region of Tra2 with MCP (MCP-RS2) is prepared to check wheather Arg–Ser-rich sequences and or other effector regions of the Tra2 protein are effectors of the splicing repression. Using Drosophila extracts this fusion protein is subjected to test its capability for dsxMS2 splicing and to repress splicing of ftzMS2-10. It was found that Arg–Ser sequences of Tra2 activates the splicing similarly like the full Tra2 protein but unable to repress splicing of ftzMS2-10. However another region of Tra2 protein named RRM-linker region able to repress splicing of ftzMS2-50 when a MCP-RRM fusion protein is subjected to the study. A mutation version (R138L) of this fusion have much less ability to repress the splicing of ftzMS2-50. These data strongly suggests that the activator and repressor activities of Tra2 are dependent on different effector sequences.
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