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The ribosomal P-site plays a vital role in all phases of translation. Initiation involves recognition of the start codon (AUG) by initiator tRNA in the P-site, elongation involves passage of many elongator tRNAs through the P site, termination involves hydrolysis of the mature polypeptide from tRNA bound to the P-site, and ribosome recycling involves release of deacylated tRNA.
Affinity label for the tRNA binding sites on the E. coli ribosome allowed the identification of A and P site proteins most likely associated with the peptidyltransferase activity; [5] labelled proteins are L27, L14, L15, L16, L2; at least L27 is located at the donor site, as shown by E. Collatz and A.P. Czernilofsky.
At the end of the initiation step, the mRNA is positioned so that the next codon can be translated during the elongation stage of protein synthesis. The initiator tRNA occupies the P site in the ribosome, and the A site is ready to receive an aminoacyl-tRNA. During chain elongation, each additional amino acid is added to the nascent polypeptide ...
The peptidyl transferase center (EC 2.3.2.12) is an aminoacyltransferase ribozyme (RNA enzyme) located in the large subunit of the ribosome.It forms peptide bonds between adjacent amino acids during the translation process of protein biosynthesis. [1]
The ribosome of E. coli has about 22 proteins in the small subunit (labelled S1 to S22) and 33 proteins in the large subunit (somewhat counter-intuitively called L1 to L36). All of them are different with three exceptions: one protein is found in both subunits (S20 and L26), [ dubious – discuss ] L7 and L12 are acetylated and methylated forms ...
The primary function of IF-2 is to transport the initiator fMet-tRNA to the P-site of the 30S ribosomal subunit. [20] The C2 domain of IF2 has a unique recognition and binding affinity towards the initiator tRNA. The IF-2 protein has been observed to form a ternary complex when interacting with GTP and fMet-tRNA. [21]
However, 23S rRNA positions (G2252, A2451, U2506, and U2585) have a significant function for tRNA binding in the P site of the large ribosomal subunit. [7] These modification nucleotides in site P can inhibit peptidyl-tRNA from binding. U2555 modification can also intervene with transferring peptidyl-tRNA to puromycin.
There are three binding sites for tRNA, the A-site, P-site and E-site (see article on protein translation for details). The core of the 60S subunit is formed by the 28S ribosomal RNA (abbreviated 28S rRNA), which is homologous to the prokaryotic 23S rRNA, which also contributes the active site (peptidyl transferase center, PTC) of the ribosome.