Characterization of ribosomal frameshift events by protein sequence analysis

Area of Science:

• Molecular Biology
• Genetics
• Biochemistry

Background:

• Cell-free protein synthesis systems utilize RNA templates for in vitro translation.
• Transfer RNAs (tRNAs) are crucial for decoding messenger RNA (mRNA) codons during translation.
• Ribosome translocation is the process of moving along the mRNA template.

Purpose of the Study:

• To investigate the mechanism of frameshift mutations induced by specific Escherichia coli tRNAs.
• To identify the codons and tRNAs involved in non-canonical ribosome translocation.
• To elucidate the molecular basis of these frameshift events.

Main Methods:

• Utilized cell-free protein synthesis with phage MS2 RNA as a template.
• Employed amino acid sequencing of tryptic peptides and cyanogen bromide fragments.
• Analyzed fragments containing the reading frame shift site to determine the exact location of the shift.

Main Results:

• Escherichia coli tRNASer3 induced a two-base translocation at alanine (GCA) codons, causing a shift to the minus-one reading frame.
• Escherichia coli tRNAThr3 induced a two-base translocation at proline (CCG) codons, also resulting in a reading frame shift.
• Identified specific tRNA-codon interactions responsible for these frameshift events.

Conclusions:

• Certain tRNAs, like tRNASer3 and tRNAThr3, can mediate frameshift mutations by interacting with non-cognate codons.
• These frameshifts are proposed to result from a two-base pair interaction between tRNA anticodons and mRNA codons.
• This mechanism highlights an unusual aspect of translational fidelity and potential for genetic variation.