Research
Examples of on-going projects are listed below:
1. Coupling transcription to pre-mRNA splicing
We have established a highly efficient in vitro system for coupling transcription by RNA polymerase II to splicing. Both functional studies with this system and analysis of purified RNAP II indicate that the mechanism for coupling transcription to splicing is the RNAP II-dependent recruitment of SR proteins and U1 snRNP to the nascent pre-mRNA. The tethering of these early commitment factors to RNAP II allows their immediate access to the nascent transcript, resulting in highly efficient spliceosome assembly and splicing.
2. Function of the human TREX complex
In yeast, the TREX complex contains the THO transcription elongation complex, which functions in the direct co-transcriptional recruitment of the mRNA export proteins Sub2 and Yra1 to nascent mRNA transcripts. We recently identified the human THO complex and showed that it specifically associates with spliced mRNA, but not with unspliced pre-mRNA. Furthermore, the human THO complex plays a role in recruiting UAP56 and Aly (the Sub2 and Yra1 counterparts) to the mRNA, but in a transcription-independent manner. Considering that splicing occurs co-transcriptionally in humans, our data indicate that recruitment of the human TREX complex to spliced mRNA is not directly coupled to transcription, but is instead coupled to transcription indirectly through splicing.
3. Molecular links between the spliceosome and the translation initiation machinery
We recently purified the spliced mRNP complex, which couples splicing to mRNA export. Other laboratories showed that this complex also functions in nonsense-mediated decay, a translation-dependent mRNA surveillance mechanism that degrades mRNAs containing non-sense codons. We identified the protein eIF4A3 as a component of the spliced mRNP. This protein is strikingly similar to eIF4A, a protein required for translation initiation. Our data indicate that eIF4A3 as well as other spliceosome components interact with the translation initiation machinery. We are investigating the significance of these interactions in non-sense mediated decay and in translation.