A top-half tDNA minihelix is a good substrate for the eubacterial CCA-adding enzyme

Area of Science:

• Molecular Biology
• Biochemistry
• RNA Biology

Background:

• The CCA-adding enzyme (ATP(CTP):tRNA nucleotidyltransferase) is crucial for tRNA maturation, catalyzing the addition and regeneration of the 3'-terminal CCA sequence.
• This CCA sequence is essential for tRNA function, serving as the amino acid attachment site and playing a role in ribosome binding.

Purpose of the Study:

• To investigate the substrate specificity of the CCA-adding enzyme beyond full-length tRNAs.
• To determine if the CCA-adding enzyme can modify DNA oligonucleotides mimicking tRNA structures.
• To elucidate the structural requirements for CCA addition to tRNA-derived DNA fragments.

Main Methods:

• Enzymatic assays using purified CCA-adding enzyme.
• Synthesis of full-length tRNA DNA and DNA oligonucleotides representing the 'top half' of tRNA (acceptor stem and TpsiC stem-loop).
• Characterization of CCA addition products using biochemical methods.

Main Results:

• The CCA-adding enzyme specifically adds a CCA terminus to synthetic full-length tRNA DNA.
• CCA addition also occurs on DNA oligonucleotides corresponding to the acceptor stem and TpsiC stem-loop of tRNA.
• CCA addition to these 'top half' DNA minihelices requires both 2' and 3' hydroxyl groups at the 3' terminus.
• The efficiency of CCA addition depends on the length of the base-paired stem and is facilitated by, but not dependent on, the TpsiC loop.

Conclusions:

• The CCA-adding enzyme exhibits specificity for tRNA-like structures, extending to DNA mimics of the tRNA 'top half'.
• These findings support the concept of independent functional and evolutionary origins for the top and bottom domains of tRNA.
• The study provides insights into the structural determinants recognized by the CCA-adding enzyme.