Investigating the function of Fal1/eIF4AIII in S. pombe

Colella, Andrea (2020). Investigating the function of Fal1/eIF4AIII in S. pombe. University of Birmingham. Ph.D.

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Abstract

The Exon Junction Complex (EJC) is a protein complex formed by a core of three proteins, eIF4AIII, MAGO, Y14, which is cotranscriptionally deposited on spliced mRNAs in mammalian cells, typically 24 nucleotides before the exon-exon boundaries. EJC deposition is believed to occur in evolutionarily divergent organisms, possibly all those that express the three core proteins. However, recent observations suggest that EJC factors are also associated with mRNAs derived from intron-less genes.

My PhD project aimed to clarify whether the EJC components are recruited on mRNAs independently of splicing in Schizosaccharomyces pombe. The data I have gathered indicate that Fal1, the ortholog of eIF4AIII in S. pombe, is associated with Pol II transcribed genes independently of the presence of an intron. To investigate whether Fal1 has a direct role in transcription or pre-mRNA processing, I engineered an Auxin-Inducible Degron (AID) system to rapidly deplete Fal1. However, I found that the application of the system causes a decrease in the Fal1 protein levels even in the absence of auxin, accompanied by severe growth defects. Therefore, I have discussed the limiting factors which might prevent the use of the AID system in S. pombe.

I have also investigated whether an EJC is formed in fission yeast. My data suggest that a mammalian-like EJC might not be formed in S. pombe, and that Fal1 can exist independently of MAGO and Y14, even though these two proteins are likely to form a heterodimer also in this organism, which in mammalian cells is sufficient to stabilize the association of eIF4AIII with splice junctions.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):