Final answer:
Initiation Factor 3 (IF3) binds to the small ribosomal subunit first, preventing premature association with the large ribosomal subunit during the early stages of the initiation of protein synthesis.
Step-by-step explanation:
The component that binds to the initiation complex first is IF3 (Initiation Factor 3). IF3 is responsible for binding to the small ribosomal subunit (30S ribosomal subunit in prokaryotes or 40S ribosomal subunit in eukaryotes) and helps to prevent its premature association with the large ribosomal subunit (50S or 60S, respectively). It remains associated with the small subunit until the initiator tRNA recognizes and binds to the AUG start codon with the help of another initiation factor, IF2, and GTP. Eventually, after the initiation complex is fully established with the mRNA, small ribosomal subunit, and initiator tRNA in place, the large ribosomal subunit is recruited to complete the initiation phase of protein synthesis, leading to the dissociation of the initiation factors.