An element in human U6 RNA destabilizes the U4/U6 spliceosomal RNA complex

Area of Science:

• Molecular Biology
• RNA Biology
• Biochemistry

Background:

• Spliceosomal RNA (e.g., U4/U6) undergoes large-scale structural changes during pre-mRNA splicing.
• ATP-dependent RNA helicases were previously thought to catalyze these structural rearrangements.
• The human U4/U6 spliceosomal RNA complex possesses potential for extensive intermolecular base pairing.

Purpose of the Study:

• To investigate the intrinsic stability of the deproteinized human U4/U6 spliceosomal RNA complex.
• To determine if RNA helicases are necessary for the dissociation of the U4/U6 complex.
• To identify cis-acting elements within the U4/U6 complex that influence its stability.

Main Methods:

• Oligonucleotide-directed RNase H cleavage to truncate U6 RNA sequences.
• Analysis of U4/U6 complex assembly and dissociation under various conditions.
• Measurement of U4/U6 complex melting temperature to assess stability.

Main Results:

• A cis-acting element in U6 RNA, corresponding to its 3' intramolecular stem, promotes U4/U6 complex dissociation.
• Oligonucleotides inhibiting U6 RNA 3' stem formation enhance U4/U6 complex assembly.
• Truncation of the U6 RNA 3' stem significantly increases the U4/U6 complex melting temperature by ~20°C.

Conclusions:

• The human U4/U6 RNA complex is intrinsically unstable due to the U6 RNA 3' stem and low activation energy for rearrangement.
• RNA helicase activity may not be essential for U4/U6 complex disassembly during spliceosome activation.
• U2-U6 RNA base pairing may stabilize the U4/U6 complex by antagonizing U6 RNA 3' stem formation.