Which factor is recognized by the translation initiation machinery at the 5' cap?

The translation initiation machinery recognizes eukaryotic initiation factors at the 5' cap of mRNA. The 5' cap is a modified guanine nucleotide added to the beginning of eukaryotic mRNA transcripts, which is essential for various aspects of mRNA metabolism, including stability, nuclear export, and translation.

Eukaryotic initiation factors bind to the 5' cap and are crucial for the recruitment of the ribosome to the mRNA. They help to facilitate the assembly of the translation initiation complex, ensuring that the ribosome is correctly positioned to begin translation at the appropriate start codon. This interaction between the initiation factors and the 5' cap is a key step in the translation process, as it allows for the recognition and processing of the mRNA by the ribosomal machinery.

Other components mentioned, such as the poly-A tail, exon junction complex, and translation termination factors, play different roles in mRNA stability, export, or termination of translation but are not directly involved in recognizing the 5' cap during the initiation of translation.