The non-universality of the genetic code is now widely appreciated. Codes differ between organisms, and certain genes are known to alter the decoding rules in a site-specific manner. Recently discovered examples of decoding plasticity are particularly spectacular. These examples include organisms and organelles with disruptions of triplet continuity during the translation of many genes, viruses that alter the entire genetic code of their hosts and organisms that adjust their genetic code in response to changing environments. In this Review, we outline various modes of alternative genetic decoding and expand existing terminology to accommodate recently discovered manifestations of this seemingly sophisticated phenomenon.
Background: Regulatory +1 frameshifting in antizyme mRNA is central for polyamine level homeostasis.Results: A nascent peptide stimulator of +1 frameshifting operates in Agaricomycete fungal antizyme mRNA.Conclusion: Frameshifting can be stimulated by nascent peptide interactions with the ribosome's peptide exit tunnel in a polyamine-dependent manner.Significance: Specific nascent peptide stimulators may be a more general and unappreciated feature of utilized ribosomal frameshifting.
Eukaryotic translation initiation involves preinitiation ribosomal complex 5 ′-to-3 ′ directional probing of mRNA for codons suitable for starting protein synthesis. The recognition of codons as starts depends on the codon identity and on its immediate nucleotide context known as Kozak context. When the context is weak (i.e., nonoptimal), leaky scanning takes place during which a fraction of ribosomes continues the mRNA probing. We explored the relationship between the context of AUG codons annotated as starts of protein-coding sequences and the next AUG codon occurrence. We found that AUG codons downstream from weak starts occur in the same frame more frequently than downstream from strong starts. We suggest that evolutionary selection on in-frame AUGs downstream from weak start codons is driven by the advantage of the reduction of wasteful out-of-frame product synthesis and also by the advantage of producing multiple proteoforms from certain mRNAs. We confirmed translation initiation downstream from weak start codons using ribosome profiling data. We also tested translation of alternative start codons in 10 specific human genes using reporter constructs. In all tested cases, initiation at downstream start codons was more productive than at the annotated ones. In most cases, optimization of Kozak context did not completely abolish downstream initiation, and in the specific example of CMPK1 mRNA, the optimized start remained unproductive. Collectively, our work reveals previously uncharacterized forces shaping the evolution of protein-coding genes and points to the plurality of translation initiation and the existence of sequence features influencing start codon selection, other than Kozak context.
Kluyveromyces marxianus is an interesting and important yeast because of particular traits like thermotolerance and rapid growth, and applications in food and industrial biotechnology. Knowing how K. marxianus responds and adapts to changing environments is important to achieve a full understanding of the its biology and to develop bioprocesses. For this, a full suite of omics tools to measure and compare global patterns of gene expression and protein synthesis is needed. Whereas transcriptome analysis by RNA-Seq quantifies mRNA abundance, ribosome profiling allows codon-resolution of translation on a genome-wide scale by deep sequencing of ribosome locations on mRNAs and is emerging as a valuable tool to study translation control of gene expression. We report here the development of a ribosome profiling method for K. marxianus and we make the procedure available as a step by step protocol. To aid in the analysis and sharing of ribosome profiling data, we also added the K. marxianus genome as well as transcriptome and ribosome profiling data to the publicly accessible GWIPS-Viz and Trips-Viz browsers. Users are able to upload custom ribosome profiling and RNA-Seq data to both browsers, therefore allowing easy analysis and sharing of data. As many studies only focus on the use of RNA-Seq to study K. marxianus in different environments, the availability of ribosome profiling is a powerful addition to the K. marxianus toolbox.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.