Structural and functional analysis of ribosome assembly factor Efg1

Area of Science:

• Molecular Biology
• Structural Biology
• Biochemistry

Background:

• Ribosome biogenesis is a complex, multi-step process essential for cell function.
• Eukaryotic ribosome assembly involves numerous transiently associated factors and RNAs.
• Efg1 is an uncharacterized protein found in early 90S pre-ribosomal particles.

Purpose of the Study:

• To determine the crystal structure of the Efg1 protein.
• To investigate the function of Efg1 in ribosome biogenesis.
• To elucidate the role of Efg1 in the early stages of small ribosomal subunit assembly.

Main Methods:

• X-ray crystallography to determine Efg1 structure.
• Genetic analysis in Saccharomyces cerevisiae.
• Analysis of 18S rRNA processing and small ribosomal subunit production.

Main Results:

• The crystal structure of Efg1 reveals a novel, elongated all-helical fold.
• Efg1 depletion blocks 18S rRNA processing at A1 and A2 sites, halting small subunit production.
• Efg1 is recruited by the 18S rRNA 5' domain, and its absence disrupts this domain's assembly and U14 snoRNA release.

Conclusions:

• Efg1 is essential for the early assembly and structural reorganization of the 18S rRNA 5' domain.
• The protein's conserved helical hairpins are critical for its function.
• Efg1's role highlights the dynamic and ordered nature of ribosome biogenesis.