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The Central Dogma

The Central Dogma

From DNA to Protein

From DNA to Protein

The flow of genetic information in cells from DNA to mRNA to protein is described by the central dogma, which states that genes specify the sequence of mRNAs, which in turn specify the sequence of amino acids making up all proteins. The decoding of one molecule to another is performed by specific proteins and RNAs. Because the information stored in DNA is so central to cellular function, it makes intuitive sense that the cell would make mRNA copies of this information for protein synthesis...

Initiation of Translation

Initiation of Translation

Initiating translation is complex because it involves multiple molecules. Initiator tRNA, ribosomal subunits, and eukaryotic initiation factors (eIFs) are all required to assemble on the initiation codon of mRNA. This process consists of several steps that are mediated by different eIFs.
First, the initiator tRNA must be selected from the pool of elongator tRNAs by eukaryotic initiation factor 2 (eIF2). The initiator tRNA (Met-tRNAi) has conserved sequence elements including modified bases at...

Leaky Scanning

Leaky Scanning

During most eukaryotic translation processes, the small 40S ribosome subunit scans an mRNA from its 5' end until it encounters the first start AUG codon. The large 60S ribosomal subunit then joins the smaller one to initiate protein synthesis. The location of the translation initiation is largely determined by the nucleotides near the start codon as there may be multiple translation initiation sites present on the mRNA. Marilyn Kozak discovered that the sequence RCCAUGG (where R stands for...

Initiation of Translation

Initiation of Translation

Initiating translation is complex because it involves multiple molecules. Initiator tRNA, ribosomal subunits, and eukaryotic initiation factors (eIFs) are all required to assemble on the initiation codon of mRNA. This process consists of several steps that are mediated by different eIFs.
First, the initiator tRNA must be selected from the pool of elongator tRNAs by eukaryotic initiation factor 2 (eIF2). The initiator tRNA (Met-tRNAi) has conserved sequence elements including modified bases at...

Regulation of Expression at Multiple Steps

Regulation of Expression at Multiple Steps

The gene expression in cells is regulated at different stages: (i) transcription, (ii) RNA processing, (iii) RNA localization, and (iv) translation. Transcriptional regulation is mediated by regulatory proteins such as transcription factors, activators, or repressors—these control gene expression by initiating or inhibiting the transcription of genes. Once a precursor or pre-mRNA is produced, it undergoes post-transcriptional modification, including 5' capping, splicing, and the addition of a...

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Multiple upstream AUG codons mediate translational control of GCN4.

P P Mueller, A G Hinnebusch

|April 25, 1986

Summary

Four upstream open-reading frames in GCN4 mRNA regulate translation. Mutations reveal specific AUG codons repress translation, with the first AUG essential for expression during starvation by antagonizing inhibitory downstream codons.

Area of Science:

Molecular Biology
Yeast Genetics
Gene Regulation

Background:

GCN4 is a yeast transcriptional activator for amino acid biosynthesis.
Its expression is primarily controlled at the translational level.
The 5' leader of GCN4 mRNA contains regulatory elements.

Purpose of the Study:

To investigate the role of upstream open-reading frames (uORFs) in GCN4 translational regulation.
To determine the specific contribution of each uORF initiation codon to translational control.
To elucidate the mechanism of GCN4 regulation under starvation conditions.

Main Methods:

Site-directed mutagenesis of initiation codons within GCN4 5' leader uORFs.
Analysis of GCN4 mRNA translation efficiency in yeast strains with mutated uORFs.

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Assessment of GCN4 expression levels under varying amino acid availability.

Main Results:

All four uORFs are essential for translational repression of GCN4.
The two 3' proximal uORFs exhibit stronger inhibitory effects than the 5' proximal uORFs.
The first uORF is unexpectedly required for efficient GCN4 expression during amino acid starvation, antagonizing the inhibitory uORFs.

Conclusions:

Yeast GCN4 translation is finely tuned by a complex interplay of four uORFs.
Differential inhibitory roles of uORFs and a positive regulatory function of the first uORF are critical for adaptive gene expression.
The GCN2 and GCD1 factors modulate uORF interactions in response to nutrient status.