Template-directed and template-free RNA synthesis by Q beta replicase

Area of Science:

• Molecular Biology
• Virology
• Biochemistry

Background:

• Q beta replicase is a viral enzyme known for RNA replication.
• Template-dependent RNA synthesis is its primary function.
• Spontaneous RNA synthesis in vitro has been observed but not fully explained.

Purpose of the Study:

• To investigate the spontaneous RNA synthesis by Q beta replicase in the absence of templates.
• To characterize the properties of these template-free RNA products.
• To elucidate the mechanism underlying template-free RNA synthesis.

Main Methods:

• In vitro incubation of Q beta replicase without added RNA templates.
• Analysis of synthesized RNA sequences and their replication rates.
• Varying enzyme and triphosphate concentrations to assess reaction dependency.
• Utilizing long closed capillaries to observe RNA growth foci.

Main Results:

• Q beta replicase spontaneously produced short RNA species (30-45 nucleotides) with no homology to viral or host RNA.
• These spontaneous RNA products exhibited significantly lower replication rates compared to template-dependent synthesis.
• Template-free RNA synthesis was sensitive to enzyme and triphosphate concentrations, unlike template-dependent synthesis.
• Heterogeneous kinetics and separate RNA growth foci were observed in template-free reactions.

Conclusions:

• The experimental evidence strongly suggests a de novo RNA synthesis mechanism by Q beta replicase in the absence of templates.
• Residual RNA contamination is an unlikely explanation for the observed template-free RNA synthesis.
• The process may involve self-instruction by non-replicatable oligonucleotides.