Publication Date

2016-05-06

Availability

Embargoed

Embargo Period

2018-05-06

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PHD)

Department

Biochemistry and Molecular Biology (Medicine)

Date of Defense

2015-12-10

First Committee Member

Antonio Barrientos

Second Committee Member

Chaitanya Jain

Third Committee Member

Murray P. Deutscher

Fourth Committee Member

Carlos T. Moraes

Fifth Committee Member

Richard Myers

Sixth Committee Member

Thomas O’Brien

Abstract

Mitoribosomes are macromachines modified from their ancestral bacterial ribosomes to specialize in the synthesis of a handful of hydrophobic proteins, essential for the biogenesis of the oxidative phosphorylation system. We have identified a conserved DEAD-box RNA helicase Mrh4 and a GTPase Mtg1 as essential mitoribosome 54S LSU assembly factors in Saccharomyces cerevisiae. Null mutants of mrh4 or mtg1 accumulate 54S assembly intermediates. The Δmrh4 mitoribosome intermediate is missing in uL9, uL16 and bL33 ribosome proteins and the assembly factor Mtg1 is not bound to it; while the mitoribosome intermediate in Δmtg1 contain Mrh4 but uL16 is highly underrepresented. We show that the stability of Mrh4 and bL33 are interdependent while overexpression of Mrh4 in the ΔbL33 mutant facilitates the generation of an apparently fully functional 54S particle. We also show that Mtg1 physically interacts with 21S rRNA and uL16. Together, this data suggest that during 54S assembly, Mrh4 promotes the incorporation of bL33, a preceding step required for the recruitment of Mtg1, which subsequently stimulates incorporation of uL16 to complete the mt-LSU assembly. Therefore, we propose a model involving the ordered recruitment of Mrh4 and Mtg1 into late-stage pre-54S particles. They are envisioned to act as RNA chaperones, presumably modifying 21S rRNA helix conformations, to fuel the sequential incorporation of late-assembly subunits.

Keywords

Mitochondria; Ribosome; Translation

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