Doctoral defence: Silva Lilleorg “Bacterial ribosome heterogeneity on the example of bL31 paralogs in Escherichia coli”

On 16 September at 10:15 Silva Lilleorg will defend her doctoral thesis “Bacterial ribosome heterogeneity on the example of bL31 paralogs in Escherichia coli” for obtaining the degree of Doctor of Philosophy (in Molecular Biology).

Supervisor:
Associate Professor Aivar Liiv, University of Tartu

Opponent:
Professor Isabella Moll, University of Vienna (Austria)

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Summary
To survive, grow and reproduce all organisms need hundreds of proteins acting as enzymes, messengers, structural components, transport and storage molecules. In addition, proteins are required to be functional at the right place, time and in sufficient amount. Therefore, protein synthesis and its regulation belong to the most central life processes. Proteins are synthesized by RNA-protein complexes called ribosomes. Experimental evidence indicates that eukaryotic and procaryotic organisms produce ribosomes with slightly different structure. The biological meaning of the phenomenon – ribosome heterogeneity – is not known. This thesis focuses on bacterial ribosome heterogeneity originating from a certain type of ribosomal proteins (paralogs) in E. coli. Paralogs have a common ancestor gene, but they encode proteins with different amino acid sequence. How does ribosome heterogeneity in ribosomal protein bL31 paralog content affect bacterial growth and translation? Analysis of ribosomal protein content showed that E. coli ribosomes are heterogeneous with respect to paralogs during fast and stationary growth phase. Subsequent work on bL31 paralogs (bL31A and bL31B) demonstrated that they are important but not equivalent for bacterial growth at lower temperatures because bL31A gives growth advantage over bL31B during fast growth. Both bL31 paralogs contribute to similar extent to translation initiation, especially to subunit joining. Interestingly, bL31A containing ribosomes are more processive and they make less errors during translation as compared to ribosomes with bL31B. This indicates that ribosome heterogeneity in bL31 paralog content may regulate translation. This thesis shed light onto functional importance of bacterial ribosome heterogeneity and thus helps us to better understand its biological meaning.

The defence will be also held in Zoom: https://ut-ee.zoom.us/j/94045246278?pwd=ZzA1c1U2bTl5WXhNVXdQZHhGTDE0Zz09. Meeting ID: 940 4524 6278, Passcode: 440046.