TRNA nucleotidyltransferase explained

tRNA nucleotidyltransferase
Ec Number:	2.7.7.56
Cas Number:	116412-36-3
Go Code:	0009022
Width:	270

In enzymology, a tRNA nucleotidyltransferase is an enzyme that catalyzes the chemical reaction

tRNA_n+1 + phosphate

\rightleftharpoons tRNA_n + a nucleoside diphosphate

where tRNA-N is a product of transcription, and tRNA Nucleotidyltransferase catalyzes this cytidine-cytidine-adenosine (CCA) addition to form the tRNA-NCCA product.

Function

Protein synthesis takes place in cytosolic ribosomes, mitochondria (mitoribosomes), and in plants, the plastids (chloroplast ribosomes). Each of these compartments requires a complete set of functional tRNAs to carry out protein synthesis. The production of mature tRNAs requires processing and modification steps^[1] such as the addition of a 3’-terminal cytidine-cytidine-adenosine (CCA). Since no plant tRNA genes encode this particular sequence, a tRNA nucleotidyltransferase must add this sequence post-transcriptionally and therefore is present in all three compartments.

In eukaryotes, multiple forms of tRNA nucleotidyltransferases are synthesized from a single gene and are distributed to different subcellular compartments in the cell. There are multiple in-frame start codons which allow for the production of variant forms of the enzyme containing different targeting information predominantly found in the N-terminal sequence of the protein (reference). In vivo experiments show that the N-terminal sequences are used as transit peptides for import into the mitochondria and plastids. Comparison studies using available tRNA nucleotidyltransferase sequences have identified a single gene coding for this enzyme in plants. Complementation studies in yeast using cDNA derived from Arabidopsis thaliana^[2] or Lupinus albus genes^[3] demonstrate the biological activity of these enzymes. The enzyme has also been shown to repair damaged or incomplete CCA sequences in yeast.^[4]

This enzyme belongs to the family of transferases, specifically those transferring phosphorus-containing nucleotide groups (nucleotidyltransferases).

Further reading

• Cudny H, Deutscher MP . 1988. 3' processing of tRNA precursors in ribonuclease-deficient Escherichia coli. Development and characterization of an in vitro processing system and evidence for a phosphate requirement. J. Biol. Chem.. 263. 1518–23. 3275667. 3. 10.1016/S0021-9258(19)57334-3. free.
• Deutscher MP, Marshall GT, Cudny H . 1988. RNase PH: an Escherichia coli phosphate-dependent nuclease distinct from polynucleotide phosphorylase. Proc. Natl. Acad. Sci. U.S.A.. 85. 4710–14. 2455297. 10.1073/pnas.85.13.4710. 13. 280505. 1988PNAS...85.4710D. free.

Notes and References

1. Hopper AK, Phizicky EM . tRNA transfers to the limelight . Genes Dev. . 17 . 2 . 162–80 . January 2003 . 12533506 . 10.1101/gad.1049103 . free .
2. MSc . Identification of proteins interacting with lupin and Arabidopsis tRNA nucleotidyltransferase . Gu J . Concordia University, Canada . 2000 . 51–55 .
3. Shanmugam K, Hanic-Joyce PJ, Joyce PB . Purification and characterization of a tRNA nucleotidyltransferase from Lupinus albus and functional complementation of a yeast mutation by corresponding cDNA . Plant Mol. Biol. . 30 . 2 . 281–95 . January 1996 . 8616252 . 10.1007/bf00020114. 8120292 .
4. Rosset R, Monier R . [Instability of the terminal 3'-hydroxy sequence of transfer RNA in microorganisms. I. Turnover of terminal AMP in Saccharomyces cerevisiae] . fr . Biochim. Biophys. Acta . 108 . 3 . 376–84 . November 1965 . 4286478 . 10.1016/0005-2787(65)90030-4 .