The process of protein synthesis in eukaryotic cells begins with a carefully orchestrated series of steps. These steps ensure that the messenger RNA (mRNA) is correctly positioned on the ribosome and that the first transfer RNA (tRNA), carrying methionine, is properly aligned with the start codon. Key occurrences involve the formation of the 43S preinitiation complex, comprising the 40S ribosomal subunit, initiation factors, and the initiator tRNA. This complex then binds to the mRNA, guided by initiation factors that recognize the 5′ cap structure. Subsequently, the complex scans the mRNA in a 5′ to 3′ direction until it encounters the start codon, AUG. Proper base-pairing between the start codon and the initiator tRNA anticodon triggers a conformational change that leads to the recruitment of the 60S ribosomal subunit, forming the complete 80S ribosome.
Efficient and accurate protein production is essential for cell survival and function. Aberrations in this initiation phase can lead to the synthesis of aberrant proteins or reduced protein levels, contributing to various diseases. Understanding these initial steps provides insights into gene expression regulation and offers potential targets for therapeutic interventions. Historically, the gradual elucidation of each initiation factor and its role in the process has built a sophisticated model of how cells control protein synthesis.