A cellular biologist is curious as to why a protein is not being expressed even though they placed the needed transcription factors and ribosomes allowing for the transcription and translation of the protein to take place in the cell. They look at the mRNA and find it is being translated and exported to the nucleus but ribosomes are not binding to it. After careful observation she finds out that the mRNA is missing its _____________. Without this of course ribosomes would have an issue binding to the mRNA and inducing translation.

In eukaryotes, the 5′ end of mRNA in eukaryotes is modified (i.e., capped) with a guanine nucleotide which is connected to mRNA via 5´→ 5´ triphosphate linkage. The five-prime cap (5′ cap) is denoted as 7-methylguanylate cap (m7G) because guanosine is methylated at the 7 position by a 7-methyl transferase. This cap acts to protect the mRNA from degradation and also is required during translation initiation in order to mediate a process known as ribosome recruitment. This process (ribosome recruitment) occurs through the association of the 43S preinitiation complex (composed of the small ribosomal subunit, eIF1, eIF1A, eIF2, eIF3 and eIF5 factors) with the 5' capped mRNA. After mRNA binding, the 43S preinitiation complex is ready to scan an initiation codon in order to start the translation.