A comparative analysis of nuclear cap binding complex proteins Cbc1, Cbc2 and putative cap binding protein Cbc3 in fission yeast

Thesis

Cap-binding complex (CBC) proteins Cbc1 and Cbc2 bind to the 7-methylguanosine (7mG) cap modification present at the 5’ end of RNA polymerase II transcripts and have been linked to a variety of functions in RNA regulation. Despite the finding that Cbc1 and Cbc2 bind the 7mG cap synergistically, there are also reports suggesting that CBC proteins can also act independently. Furthermore, recently a new cap binder, named Cbc3, has been discovered, with its function in the context of CBC yet to be discovered. In this thesis, S. pombe Cbc1, Cbc2 and Cbc3 are compared with respect to their co-transcriptional recruitment, interacting proteins, and the subsequent effect of their depletion on the transcriptome. Cbc1 and Cbc2 depletions resulted in diverging differential expression profiles and changes in RNA processing. Differences could not be attributed to transcriptional changes. A genetic screen showed that these genes also have diverging interactions with RNA surveillance factors. Interestingly, Cbc1 depletion, and not Cbc2, was found to rescue readthrough transcription associated with a Dhp1 temperature- sensitive mutation. This thesis thus provides data supportive of Cbc1 having a Cbc2- independent, anti-cleavage role. On the other hand, S. pombe Cbc3 was found to facilitate the recruitment of elongation factor Paf1 to protein-coding (pc) genes that are longer than ~500 bases. Furthermore, Cbc3 deletion resulted in a mild hindrance of RNA export. Taken together, my findings point to inherent CBC-independent functions for Cbc1 and Cbc2. While Cbc3 is important for transcription elongation and nuclear export, it is unlikely that it forms the basis of an alternative CBC.

Authors: Ulgen, DH

• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: Cbc1; RNA; Cap binding complex; Cbc3; transcription; Cbc2
• Subjects: RNA biology; Molecular biology; Biochemistry