tRNAs Marked with CCACCA Are Targeted for Degradation.
Wilusz, Jeremy E. 1,*; Whipple, Joseph M. 2; Phizicky, Eric M. 2; Sharp, Phillip A. 1
[Article] Science. 334(6057):817-821, November 11, 2011.

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: The CCA-adding enzyme [ATP(CTP):tRNA nucleotidyltransferase] adds CCA to the 3' ends of transfer RNAs (tRNAs), a critical step in tRNA biogenesis that generates the amino acid attachment site. We found that the CCA-adding enzyme plays a key role in tRNA quality control by selectively marking structurally unstable tRNAs and tRNA-like small RNAs for degradation. Instead of adding CCA to the 3' ends of these transcripts, CCA-adding enzymes from all three kingdoms of life add CCACCA. In addition, hypomodified mature tRNAs are subjected to CCACCA addition as part of a rapid tRNA decay pathway in vivo. We conjecture that CCACCA addition is a universal mechanism for controlling tRNA levels and preventing errors in translation.

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