'2A-Like' Signal Sequences Mediating Translational Recoding: A Novel Form of Dual Protein Targeting.

We report the initial characterization of an N-terminal oligopeptide '2A-like' sequence that is able to function both as a signal sequence and as a translational recoding element. Owing to this translational recoding activity, two forms of nascent polypeptide are synthesized: (i) when 2A-mediated translational recoding has not occurred: the nascent polypeptide is fused to the 2A-like N-terminal signal sequence and the fusion translation product is targeted to the exocytic pathway, and, (ii) a translation product where 2A-mediated translational recoding has occurred: the 2A-like signal sequence is synthesized as a separate translation product and, therefore, the nascent (downstream) polypeptide lacks the 2A-like signal sequence and is localized to the cytoplasm. This type of dual-functional signal sequence results, therefore, in the partitioning of the translation products between the two sub-cellular sites and represents a newly described form of dual protein targeting.

Lost in translation: The biogenesis of non-LTR retrotransposon proteins.

"Young" APE-type non-LTR retrotransposons (non-LTRs) typically encode two open reading frames (ORFs 1 and 2). The shorter ORF1 translation product (ORF1p) comprises an RNA binding activity, thought to bind to non-LTR transcript RNA, protect against nuclease degradation and specify nuclear import of the ribonuclear protein complex (RNP). ORF2 encodes a multifunctional protein (ORF2p) comprising apurinic/apyrimidinic endonuclease (APE) and reverse-transcriptase (RT) activities, responsible for genome replication and re-integration into chromosomal DNA.

The committee for advanced therapies' of the European Medicines Agency reflection paper on management of clinical risks deriving from insertional mutagenesis.

In the European Union, the Committee for Advanced Therapies of the European Medicines Agency takes the lead in the scientific assessment for marketing authorization applications for advanced therapy medicinal products, which include gene therapy medicinal products, somatic cell therapy medicinal products, and tissue-engineered products. The Committee for Advanced Therapies also takes the lead in defining the scientific framework for the quality, nonclinical and clinical development of such products. This reflection paper represents the Committee's current thinking on management of clinical risks deriving from insertional mutagenesis.

APE-type non-LTR retrotransposons of multicellular organisms encode virus-like 2A oligopeptide sequences, which mediate translational recoding during protein synthesis.

2A oligopeptide sequences ("2As") mediate a cotranslational recoding event termed "ribosome skipping." Previously we demonstrated the activity of 2As (and "2A-like sequences") within a wide range of animal RNA virus genomes and non-long terminal repeat retrotransposons (non-LTRs) in the genomes of the unicellular organisms Trypanosoma brucei (Ingi) and T. cruzi (L1Tc).

Genome organization and translation products of Providence virus: insight into a unique tetravirus.

Providence virus (PrV) is a member of the family Tetraviridae, a family of small, positive-sense, ssRNA viruses that exclusively infect lepidopteran insects. PrV is the only known tetravirus that replicates in tissue culture. We have analysed the genome and characterized the viral translation products, showing that PrV has a monopartite genome encoding three ORFs: (i) p130, unique to PrV and of unknown function; (ii) p104, which contains a read-through stop signal, producing an N-terminal product of 40 kDa (p40) and (iii) the capsid protein precursor (p81).

2A to the fore - research, technology and applications.

The 2A region of the foot-and-mouth disease virus (FMDV) encodes a short sequence that mediates self-processing by a novel translational effect. Translation elongation arrest leads to release of the nascent polypeptide and re-initiation at the next in-frame codon. In this way discrete translation products are derived from a single open reading frame.

Inhibition of 2A-mediated 'cleavage' of certain artificial polyproteins bearing N-terminal signal sequences.

Where 2A oligopeptide sequences occur within ORFs, the formation of the glycyl-prolyl peptide bond at the C-terminus of (each) 2A does not occur. This property can be used to concatenate sequences encoding several proteins into a single ORF: each component of such an artificial polyprotein is generated as a discrete translation product. 2A and '2A-like' sequences have become widely utilised in biotechnology and biomedicine.

Dissection of a co-translational nascent chain separation event.

Some RNA and protein sequences are capable of directing changes to the course of translation from that expected from the mRNA sequence, and this process is termed translational 'recoding'. 'CHYSEL' peptides are approximately 19-amino-acid sequences found in many viral genomes. When translated at internal portions of polypeptides, they yield co-translational separation of the nascent chain at their C-termini.

Site-specific release of nascent chains from ribosomes at a sense codon.

"2A" oligopeptides are autonomous elements containing a D(V/I)EXNPGP motif at the C terminus. Protein synthesis from an open reading frame containing an internal 2A coding sequence yields two separate polypeptides, corresponding to sequences up to and including 2A and those downstream. We show that the 2A reaction occurs in the ribosomal peptidyltransferase center.

Occurrence, function and evolutionary origins of '2A-like' sequences in virus genomes.

2A is an oligopeptide sequence mediating a ribosome 'skipping' effect, producing an apparent 'cleavage' of polyproteins. First identified and characterized in picornaviruses, '2A-like' sequences are found in other mammalian viruses and a wide range of insect viruses. Databases were analysed using a motif conserved amongst 2A/2A-like sequences.

E unum pluribus: multiple proteins from a self-processing polyprotein.

Many applications of genetic engineering require transformation with multiple (trans)genes, although to achieve these using conventional techniques can be challenging. The 2A oligopeptide is emerging as a highly effective new tool for the facile co-expression of multiple proteins in a single transformation step, whereby a gene encoding multiple proteins, linked by 2A sequences, is transcribed from a single promoter. The polyprotein self-processes co-translationally such that each constituent protein is generated as a discrete translation product.

Skipping the co-expression problem: the new 2A "CHYSEL" technology.

The rapid progress in the field of genomics is increasing our knowledge of multi-gene diseases. However, any realistic hope of gene therapy treatment for those diseases needs first to address the problem of co-ordinately co-expressing several transgenes. Currently, the use of internal ribosomal entry sites (IRESs) is the strategy chosen by many researchers to ensure co-expression.

Targeting of proteins derived from self-processing polyproteins containing multiple signal sequences.

The 18aa 2A self-cleaving oligopeptide from foot-and-mouth disease virus can be used for co-expression of multiple, discrete proteins from a single ORF. 2A mediates a co-translational cleavage at its own C-terminus and is proposed to manipulate the ribosome into skipping the synthesis of a specific peptide bond (producing a discontinuity in the peptide backbone), rather than being involved in proteolysis. To explore the utility of the system to target discrete processing products, self-processing polyproteins comprising fluorescent proteins flanking 2A were constructed, permutating both the type of signal sequence and the location within the polyprotein.

Construction and characterization of pentacistronic retrovirus vectors.

The picornavirus foot-and-mouth disease virus 2A sequence was combined with three different internal ribosome entry segments to construct and characterize three independent pentacistronic retroviruses of different sizes. Efficient co-expression of the five proteins was successful and titres obtained for these pentacistronic virus vectors (final genome size approximately 7.9 kb) were comparable to those of vector systems with shorter genomes.

Co-translational, intraribosomal cleavage of polypeptides by the foot-and-mouth disease virus 2A peptide.

During co-translational protein import into the endoplasmic reticulum ribosomes are docked onto the translocon. This prevents inappropriate exposure of nascent chains to the cytosol and, conversely, cytosolic factors from gaining access to the nascent chain. We exploited this property of co-translational translocation to examine the mechanism of polypeptide cleavage by the 2A peptide of the foot-and-mouth disease virus.