# Eukaryotic Ribosome Assembly

> **NIH NIH R35** · UNIVERSITY OF TEXAS AT AUSTIN · 2020 · $568,140

## Abstract

PI: Arlen W Johnson
Summary
 Ribosomes are responsible for the rapid and accurate production of all proteins
in cells in all forms of life on earth. The ability of these molecular machines to carry out
faithful translation depends on their complex structure that allows dynamic interaction
with ligands. The mature ribosome in eukaryotic cells is composed of two parts, the
large 60S subunit that carries out polypeptide synthesis and the small 40S subunit that
decodes mRNA. The assembly of a eukaryotic ribosome involves over 200 accessory
assembly factors, whose function, in many cases, is still unknown. Considering the
complexity of ribosome structure and function and its critical role in decoding our genetic
information, ensuring their correct assembly would seem a necessary but daunting task
for cells. Lately, considerable interest has been focused on mechanisms of quality
control in the ribosome biogenesis pathway. This proposal focuses on two distinct topics
within ribosome assembly; (1) completion of the peptidyl transferase center of the 60S
subunit and the mechanisms for assessing its functional integrity and (2) the transition
from the early 90S pre-ribosomal precursor to the pre-40S precursor.
 This proposal is directed at understanding the quality control mechanisms that
assess the functional and structural integrity of the peptidyl transferase center of the
subunit, upon insertion of ribosomal protein Rpl10. This proposal builds on our recent
determination of the atomic structure of a preribosome and release of two factors, Tif6
and Nmd3. The release of Nmd3 and Tif6 is dependent on the two GTPases Efl1 and
Lsg1 and constitutes the primary quality control check point in during 60S maturation. In
humans, defects in the quality control step lead to T-cell acute lymphoblastic leukemia
and Shwachman-Diamond syndrome.
 Assembly of the small ribosomal subunit involves stepwise cotranscriptional
assembly of the 90S particle, a large protein-RNA complex, scaffolded on U3-snoRNA.
However, the presence of U3 is mutually incompatible with the final folded structure of
small subunit RNA and must be removed once transcription of the RNA is complete and
the 90S particle has fully assembled. The transition from the 90S to pre-40S is poorly
understood. We propose that the displacement of U3 by the RNA helicase Dhr1 is a
primary event that drives the transition of the 90S into the pre-40S particle. We will
determine how the activity of Dhr1 is regulated to ensure the timely release of U3.

## Key facts

- **NIH application ID:** 10004112
- **Project number:** 5R35GM127127-03
- **Recipient organization:** UNIVERSITY OF TEXAS AT AUSTIN
- **Principal Investigator:** Arlen W JOHNSON
- **Activity code:** R35 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2020
- **Award amount:** $568,140
- **Award type:** 5
- **Project period:** 2018-09-14 → 2023-08-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10004112

## Citation

> US National Institutes of Health, RePORTER application 10004112, Eukaryotic Ribosome Assembly (5R35GM127127-03). Retrieved via AI Analytics 2026-05-23 from https://api.ai-analytics.org/grant/nih/10004112. Licensed CC0.

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