Amino acid starvation leads to the binding of uncharged tRNAs to the ribosomal A site; this triggers a sequence of events that begins with the binding of an enzyme called stringent factor (RelA protein) to the ribosome. 

TLS Online TPP Program

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#Unit 3. Fundamental Processes

TLS Online TPP Program

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#Unit 3. Fundamental Processes

TLS Online TPP Program

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#Unit 3. Fundamental Processes

TLS Online TPP Program

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#Unit 3. Fundamental Processes

IF1 prevents tRNAs from binding to the portion of the small subunit that will become part of the A-site.

†IF2 is a GTPase that interacts with three key components of the initiation machinery: the small subunit, IF1, and the charged initiator tRNA (fMet-tRNAi f-Met). By interacting with these components, IF2 facilitates the association of fMet-tRNAi f-Met with the small subunit and prevents other charged tRNAs from associating with the small subunit.

† IF3 binds to the small subunit and blocks it from reassociating with a large subunit. Because initiation requires a free small subunit, the binding of IF3 is critical for a new cycle of translation. 

TLS Online TPP Program

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#Unit 3. Fundamental Processes

TLS Online TPP Program

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#Unit 3. Fundamental Processes

binding by a ribosome, many prokaryotic ORFs contain a short sequence upstream (on the 5’ side) of the start codon called the ribosome binding site (RBS). This element is also referred to as a polypurine stretch Shine–Dalgarno sequence.