Translational efficiency of a non-AUG initiation codon is significantly affected by its sequence context in yeast.

Previous studies have shown that translation of mrna for yeast glycyl-tRNA synthetase is alternatively initiated from UUG and a downstream AUG initiation codon. Evidence presented here shows that unlike an AUG initiation codon, efficiency of this non-AUG initiation codon is significantly affected by its sequence context, in particular the nucleotides at positions -3 to -1 relative to the initiation codon. A/A/R (R represents A Or G) and C/G/C appear to be the most and least favorable sequences at these positions, respectively.

NF-kappaB-dependent induction of microRNA miR-146, an inhibitor targeted to signaling proteins of innate immune responses.

Activation of mammalian innate and acquired immune responses must be tightly regulated by elaborate mechanisms to control their onset and termination. MicroRNAs have been implicated as negative regulators controlling diverse biological processes at the level of posttranscriptional repression. Expression profiling of 200 microRNAs in human monocytes revealed that several of them (miR-146a/b, miR-132, and miR-155) are endotoxin-responsive genes.

Redundancy of non-AUG initiators. A clever mechanism to enhance the efficiency of translation in yeast.

It was recently shown that ALA1, the only alanyl-tRNA synthetase gene in Saccharomyces cerevisiae, uses two successive ACG triplets as the translation initiators for its mitochondrial form. Evidence presented here argues that the second ACG triplet not only acts as a remedial initiation site for scanning ribosomes that skip the first ACG, but also enhances the activity of the preceding initiator by providing a preferable "A" at its relative position +4. Therefore, ALA1 constructs with redundant ACG initiators exhibit stronger complementing activity and express a higher level of protein than do those with a single ACG initiator.

Translation initiation from a naturally occurring non-AUG codon in Saccharomyces cerevisiae.

Although previous studies have already shown that both cytoplasmic and mitochondrial activities of glycyl-tRNA synthetase are provided by a single gene, GRS1,in the yeast Saccharomyces cerevisiae, the mechanism by which this occurs remains unclear. Evidence presented here indicates that this bifunctional property is actually a result of two distinct translational products alternatively generated from a single transcript of this gene. Except for an amino-terminal 23-amino acid extension, these two isoforms have the same polypeptide sequence and function exclusively in their respective compartments under normal conditions.

Mitochondrial form of a tRNA synthetase can be made bifunctional by manipulating its leader peptide.

Previous studies showed that yeast VAS1 encodes both the cytoplasmic and mitochondrial forms of valyl-tRNA synthetase (ValRS), using alternative transcription and translation. The ValRS isoforms have identical polypeptide sequences, except for a 46-amino acid leader peptide that functions as a mitochondrial targeting signal. Although the two forms of the enzyme exhibit indistinguishable tRNA specificities in vitro, they cannot substitute for each other in vivo because of their different localizations.