Initiation complex assembly

Asano, K., Shalev, A., Phan, L., Nielsen, K., Clayton, J., Valasek, L., Donahue, T. F., and Hinnebusch, A. G. (2001). Multiple roles for the carboxyl terminal domain of eIF5 in translation initiation complex assembly and GTPase activation. EMBOJ. 20, 2326—2337. 

Given that these proteins have properly assembled, the initiation complex is ready to start transcription. How does the enzyme get started A component of TFIID, again a multi-subunit complex TFIIH, unwinds the DNA and phosphorylates serine-5 of the C-terminal tail (CTD) of the largest polymerase subunit (Rpbl). Serine-5 phosphorylation and phosphorylation of serine-2 (by pTEFb) are required to release the enzyme from the other components of the initiation complex and to start RNA synthesis. 

After attachment of amino acids to tRNA, the amino acids are assembled beginning with the amino terminus and proceeding in the direction of the carboxy terminus. The ribosome is the machinery that translates the mRNA into protein. The ribosome is a very complex protein that contains ribosomal RNA as a functional and structural component. The ribosome assembles around the mRNA, and the cap and other signals allow alignment of the mRNA into the correct position. The initial assembly of the mRNA into the ribosome requires association of the small ribosomal subunit with an initiator tRNA (Met or fMet). Small is a misstatement, because the small ribosomal subunit is a large, complex assembly of numerous smaller proteins—it s just smaller than the... 

By 1960 it seemed likely that vesicles (sealed membrane preparations) were essential for ATP formation to occur. R.J.P. Williams (1959-1961 see 1993) postulated that complex assemblies of catalysts, as in the cytochrome chain, would allow spatial separation of reaction products within the mitochondrial membrane. The initial site of reaction with... 

C. Eukaryotic transcription is more complex than in prokaryotes, mainly in terms of the nature of the RNA polymerases, the assembly of the pre-initiation complex, and the need for processing eukaryotic RNAs. 

C. The first step in translation of an mRNA is assembly of an initiation complex of... 

Figure 12-2. Formation of the initiation complex for protein synthesis. Several eukaryotic initiation factors (elFs) ensure proper assembly at each step. The initiator Met-tRNA is bound in the peptidyl site of the SOS complex with its anticodon (black stripes) base paired to the AUG start codon (gray box) of the mRNA.

Streptomycin, gentamicin, and other aminoglycosides interfere with assembly of the SOS initiation complex and promote incorrect base pairing. 

Initiation of protein synthesis involves the assembly of the components of the translation system before peptide bond formation occurs. These components include the two ribosomal subunits, the mRNA to be translated, the aminoacyl-tRNA specified by the first codon in the message, GTP (which provides energy for the process), and initiation factors that facilitate the assembly of this initiation complex (see Figure 31.13). [Note In prokaryotes, three initiation factors are known (IF-1, IF-2, and IF-3), whereas in eukary- otes, there are at least ten (designated elF to indicate eukaryotic origin).] There are two mechanisms by which the ribosome recognizes the nucleotide sequence that initiates translation ... 

Roeder, R. G., The complexities of eukaryotic transcription initiation Regulation of preinitiation complex assembly. Trends Biochem. Sci. 16 402-407, 1991. 

Fig. 2 The conformational cycle of SNAREs. SNAREs cycle between two extreme conformations, the unstructured monomeric SNAREs and the fully assembled cis-SNARE complexes. Initially, SNAREs on the membranes destined to fuse establish trans-SNARE complexes between the opposed membranes. Proceeding SNARE complex assembly forces the membranes tightly together enforcing membrane fusion. The resulting cis-SNARE complexes are disassembled into free SNAREs by the ATPase NSF and its co-factor, a process that consumes ATP and fuels the SNAREs with energy for undergoing a new SNARE cycle (for details see text).

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