Multiple Parallel Pathways of Translation Initiation on the CrPV IRES

Area of Science:

• Molecular Biology
• Virology
• Biochemistry

Background:

• Eukaryotic translation is complex and finely regulated.
• Viruses, such as the cricket paralysis virus (CrPV), utilize internal ribosome entry sites (IRESs) to initiate protein synthesis, often bypassing the need for canonical initiation factors.

Purpose of the Study:

• To observe the real-time process of translation initiation and the transition to elongation using the CrPV IRES.
• To identify and characterize the distinct pathways involved in 80S ribosomal complex assembly and reading frame selection.

Main Methods:

• Single-molecule fluorescence spectroscopy was employed to track the CrPV IRES, ribosomal subunits (40S and 60S), and transfer RNA (tRNA) in real time.
• Analysis of complex assembly dynamics and intermediate states during translation initiation.

Main Results:

• Multiple parallel pathways for translation initiation were identified.
• Two distinct pathways leading to elongation-competent 80S:CrPV IRES complexes were distinguished.
• The arrival of the first elongator tRNA was found to define the reading frame, strongly favoring the 0 frame over the +1 frame.

Conclusions:

• Translation initiation, even in simplified viral systems, involves an intricate network of reactions.
• The binding of the first tRNA is a critical determinant for establishing the correct reading frame during viral translation initiation.