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The first step in initiation is formation of the pre-initiation complex, 48S PIC. The small ribosomal subunit and various eukaryotic initiation factors are recruited to the mRNA 5′ TL and to form the 48S PIC complex, which scans 5′ to 3′ along the mRNA transcript, inspecting each successive triplet for a functional start codon.
Translation is one of the key energy consumers in cells, hence it is strictly regulated. Numerous mechanisms have evolved that control and regulate translation in eukaryotes as well as prokaryotes. Regulation of translation can impact the global rate of protein synthesis which is closely coupled to the metabolic and proliferative state of a cell.
Initiation of translation is regulated by the accessibility of ribosomes to the Shine-Dalgarno sequence. This stretch of four to nine purine residues are located upstream the initiation codon and hybridize to a pyrimidine-rich sequence near the 3' end of the 16S RNA within the 30S bacterial ribosomal subunit . [ 1 ]
A eukaryotic cell has a nucleus that separates the processes of transcription and translation. Eukaryotic transcription occurs within the nucleus where DNA is packaged into nucleosomes and higher order chromatin structures. The complexity of the eukaryotic genome necessitates a great variety and complexity of gene expression control.
Inside eukaryotic cells, there is a balance between the processes of translation and mRNA decay. Messages that are being actively translated are bound by ribosomes , the eukaryotic initiation factors eIF-4E and eIF-4G , and poly(A)-binding protein . eIF-4E and eIF-4G block the decapping enzyme ( DCP2 ), and poly(A)-binding protein blocks the ...
Translation promotes transcription elongation and regulates transcription termination. Functional coupling between transcription and translation is caused by direct physical interactions between the ribosome and RNA polymerase ("expressome complex"), ribosome-dependent changes to nascent mRNA secondary structure which affect RNA polymerase activity (e.g. "attenuation"), and ribosome-dependent ...
An upstream open reading frame (uORF) is an open reading frame (ORF) within the 5' untranslated region (5'UTR) of an mRNA. uORFs can regulate eukaryotic gene expression. [1] [2] Translation of the uORF typically inhibits downstream expression of the primary ORF. However, in some genes such as yeast GCN4, translation of specific uORFs may ...
Translation started by an internal ribosome entry site (IRES), which bypasses a number of regular eukaryotic initiation systems, can have a non-methinone start with GCU or CAA codons. [23] Mammalian cells can initiate translation with leucine using a specific leucyl-tRNA that decodes the codon CUG. This mechanism is independent of eIF2.