Transcriptome-wide analysis of the function of Ded1 in translation preinitiation complex assembly in a reconstituted...

Area of Science:

• Molecular Biology
• Genetics
• Biochemistry

Background:

• Translation initiation is a critical regulatory step in gene expression.
• The DEAD-box ATPase Ded1 is an essential translation initiation factor, but its precise mechanism of action remains debated.
• Understanding Ded1's role is crucial for deciphering translational control, especially for mRNAs with complex regulatory elements.

Approach:

• Developed Rec-Seq, a deep sequencing-based method for in vitro monitoring of 48S pre-initiation complex (PIC) formation on all mRNAs simultaneously.
• Rec-Seq isolates early translation initiation events in a reconstituted system, free from other cellular components.
• Applied Rec-Seq to investigate the function of Ded1 and eIF4A in translation initiation.

Key Points:

• Ded1 promotes 48S PIC formation on the start codons of over 1000 native mRNAs, especially those with long, structured 5'UTRs.
• Rec-Seq results validate in vivo findings from ribosome profiling of *ded1* mutants, confirming Ded1's core translation functions in vitro.
• Ded1's mechanism involves directly promoting mRNA recruitment to the 43S PIC and scanning, not by repressing alternative start codons.
• eIF4A is essential for PIC assembly on nearly all mRNAs, irrespective of 5'UTR complexity, unlike Ded1's preferential role.

Conclusions:

• Rec-Seq provides a powerful tool to study translation initiation dynamics in a purified system.
• Ded1's primary function is to facilitate start codon recognition on a wide range of mRNAs, particularly those with challenging 5'UTRs.
• The findings clarify Ded1's mechanism, highlighting its role in promoting mRNA selection and scanning during translation initiation.