Answer: start codon AUG of mRNA
Step-by-step explanation:
The ribosomal assembly consist of two receptor sites, the P and A sites. The P site carries the peptidyl-tRNA, the growing peptide chain while the A site carries the new incoming tRNA with the amino acid to be added next.
The mRNA signal the initiation process with it start codon AUG. Because the start codon AUG codes for the amino acid methionine. A tRNA attach to methionine (tRNA-Met) binds to the start codon. The anti-codon UAC of the met-tRNA is correctly base pairing with the AUG codon on mRNA.