L1Tc non-LTR retrotransposons from Trypanosoma cruzi contain a functional viral-like self-cleaving 2A sequence in frame with the active proteins they encode

Abstract

A comparative analysis of 40 Trypanosoma cruzi L1Tc elements showed that the 2A self-cleaving sequence described in viruses is present in them. Of these elements, 72% maintain the canonical 2A motif (DxExNPGP). A high percentage has a conserved point mutation within the motif that has not been previously described. In vitro and in vivo expression of reporter polyproteins showed that the L1Tc2A sequence is functional. Mutations within certain L1Tc2A sequences affect the efficiency of the cleavage. The data indicate that the L1Tc2A sequence may be influencing the L1Tc enzymatic machinery determining the composition and level of the translated products. The residues located immediately upstream of the 2A consensus sequence increase the cleaving efficiency and appear to stabilize the relative amount of translated products.

Site-Specific Release of Nascent Chains from Ribosomes at a Sense Codon

“…Active "2A-like" sequences are also found in a number of insect viruses, in type C rotaviruses, and in Trypanosoma species repeated sequences (4,15,22,27,34,50; http://www .st-andrews.ac.uk/ryanlab/2A_2Alike.pdf). We set out to gain deeper insight into the 2A reaction, specifically, to determine if it occurs at the ribosomal peptidyltransferase center and to identify cellular factors that influence the reaction.…”

“…2A peptides occur in many viral genomes and are key elements in the control of their protein biogenesis (4,14,15,20,27,34,40,50). Functional 2A peptides are also found in repeated sequences within trypanosome genomes (16,22). Remarkably, 2A peptides exert their effect in all of the eukaryotic systems in which they have been tested, indicating that they interact with highly conserved features of the eukaryotic cell.…”

The L1Tc non-LTR retrotransposon of Trypanosoma cruzi contains an internal RNA-pol II-dependent promoter that strongly activates gene transcription and generates unspliced transcripts

“…However, it cannot be excluded that other L1Tc sequences located downstream of Pr77 are required for ribosome stabilization. It has been described that the potentially active L1Tc elements contain an in vivo functional viral-like 2A self-cleaving sequence (L1Tc2A) located downstream of Pr77 and in frame with the proteins that L1Tc encodes (46). The present data suggest that the mechanism of polypeptide cleavage by the L1Tc2A peptide is co-translational and could influence the composition and probably the relative abundance of the proteins that compose the L1Tc mobilization machinery (46).…”

Dissection of a co-translational nascent chain separation event

“…In addition to aphthoviruses, active CHYSEL peptides are encoded within the genomes of other picornaviruses (cardioviruses) as well as a number of other single-and double-stranded RNA viruses [2,5,[8][9][10][11][12][13]. The only non-viral sequences so far shown to have CHYSEL activity occur in repeated sequences within the genomes of trypanosomes [14]. Recent work on the occurrence and evolutionary origins of viral CHYSEL sequences suggests that these sequences appeared independently in the evolution of different viruses [2].…”