The tailing happens in a template independent manner.what is the meaning of the template independent manner ?
Answers
The 3'-terminal CCA nucleotide sequence (positions 74-76) of transfer RNA is essential for amino acid attachment and interaction with the ribosome during protein synthesis. The CCA sequence is synthesized de novo and/or repaired by a template-independent RNA polymerase, 'CCA-adding enzyme', using CTP and ATP as substrates. Despite structural and biochemical studies, the mechanism by which the CCA-adding enzyme synthesizes the defined sequence without a nucleic acid template remains elusive. Here we present the crystal structure of Aquifex aeolicus CCA-adding enzyme, bound to a primer tRNA lacking the terminal adenosine and an incoming ATP analogue, at 2.8 A resolution. The enzyme enfolds the acceptor T helix of the tRNA molecule. In the catalytic pocket, C75 is adjacent to ATP, and their base moieties are stacked. The complementary pocket for recognizing C74-C75 of tRNA forms a 'protein template' for the penultimate two nucleotides, mimicking the nucleotide template used by template-dependent polymerases. These results are supported by systematic analyses of mutants. Our structure represents the 'pre-insertion' stage of selecting the incoming nucleotide and provides the structural basis for the mechanism underlying template-independent RNA polymerization
Poly A (poly adenine) tail is added to premature messenger RNA (pre-mRNA).
Explanation:
For addition of poly (A) tail there is no need of template DNA. Generally for the synthesis of messenger RNA or DNA in replication, there is a need of template to synthesize new strand. Poly A polymerase is the enzyme that will add poly A tail to the 3' end of mRNA. It is important for export of mRNA to cytoplasm, for translation as well as for stability of mRNA.