A eubacterial origin for the human tRNA nucleotidyltransferase?

Area of Science:

• Molecular Biology
• Enzymology
• Evolutionary Biology

Background:

• Transfer RNA (tRNA) CCA-termini are essential for protein synthesis and are maintained by tRNA nucleotidyltransferases.
• Distinguishing CCA-adding enzymes from poly(A) polymerases within the nucleotidyltransferase superfamily is challenging due to sequence similarities.
• Lack of sequence data for animal CCA-adding enzymes hindered gene identification.

Purpose of the Study:

• To identify and characterize the human CCA-adding enzyme.
• To investigate the evolutionary origins of animal CCA-adding enzymes.

Main Methods:

• BLAST search using yeast tRNA nucleotidyltransferase against human sequences.
• Cloning and biochemical characterization of the human CGI-47 protein.
• Sequence alignment and phylogenetic analysis (neighbor-joining tree) of CCA-adding enzymes.

Main Results:

• The human gene transcript CGI-47 was identified as encoding a bona fide CCA-adding enzyme, not a poly(A) polymerase.
• Biochemical characterization confirmed the enzymatic activity of the human CGI-47 protein.
• Phylogenetic analysis indicated that animal CCA-adding enzymes are more closely related to eubacterial enzymes than to plant or fungal counterparts.

Conclusions:

• The human CGI-47 gene encodes a functional CCA-adding enzyme, enabling the identification of homologous animal genes.
• The evolutionary origin of animal nuclear CCA genes likely stems from endosymbiotic events related to mitochondria, suggesting a eubacterial origin.