Evidence for an RNA pseudoknot loop-helix interaction essential for efficient -1 ribosomal frameshifting

Area of Science:

• Molecular Biology
• RNA Structure and Function
• Genetics

Background:

• RNA pseudoknots are crucial for biological processes, particularly at ribosomal frameshifting sites.
• Infectious bronchitis virus (IBV) and mouse mammary tumor virus (MMTV) pseudoknots exemplify distinct structural types influencing frameshifting efficiency.

Purpose of the Study:

• To investigate sequence manipulations for converting short, non-functional IBV-derived pseudoknots into efficient, kinked frameshifters.
• To bypass the requirement for a long stem 1 (11 bp) in IBV pseudoknots.

Main Methods:

• Sequence manipulation of IBV-derived pseudoknots.
• Introduction of an adenine residue at the stem 1-stem 2 junction.
• Modification of the terminal nucleotide of loop 2.
• Mutational analysis of loop-helix interactions.

Main Results:

• A single adenine insertion at the stem 1-stem 2 junction was insufficient for functional frameshifting.
• Efficient frameshifting was restored by changing the loop 2 terminal nucleotide from G to A.
• A specific loop-helix contact involving the loop 2 terminal adenine and stem 1 nucleotides was identified as essential.
• This requirement for a terminal A was dependent on loop 2 length.

Conclusions:

• Short, kinked frameshifter pseudoknots can be engineered through specific sequence modifications.
• A loop-helix interaction is critical for efficient frameshifting in pseudoknots with short loop 2.
• These findings provide insights into the structural requirements for RNA-mediated ribosomal frameshifting.