Biology of Trypanosoma cruzi Retrotransposons: From an Enzymatic to a Structural Point of View

INTRODUCTION: An important portion of the Trypanosoma cruzi genome is composed of mobile genetic elements, which are interspersed with genes on all chromosomes. The L1Tc non-LTR retrotransposon and its truncated version NARTc are the most highly represented and best studied of these elements. L1Tc is actively transcribed in all three forms of the Trypanosoma parasite and encodes the proteins that enable it to autonomously mobilize. This mini review discusses the enzymatic properties of L1Tc that enable its mobilization and possibly the mobilization of other non-autonomous retrotransposons in Trypanosoma. We also briefly review the Hepatitis Delta Virus-like autocatalytic and 2A self-cleaving viral-like sequences contained in L1Tc that regulate post-transcriptional properties such as relative protein abundance and mRNA stability. Special emphasis is placed on the Pr77 dual system, which is based on the RNA pol II-dependent internal promoter of L1Tc and NARTc and the HDV-like ribozyme activity encoded by the first 77 nucleotides of the element’s DNA and RNA. The high degree of conservation of the Pr77 sequence, referred to as the “Pr77-hallmark”, among different trypanosomatid retroelements suggests that these mobile elements are responsible for the distribution of regulatory sequences within the genome they inhabit. CONCLUSION: We also discuss how the involvement of L1Tc and NARTc in the gene regulatory processes of these parasites could justify their domestication and long-term coexistence in these ancient organisms.