Authors

K Záhonová¹; Z Fussy²; A Albanaz³; A Butenko¹; J Votýpka⁴; A Kostygov³; A Kachale¹; F Fakih¹; Z Paris¹; V Yurchenko³; J Lukes¹;  ¹ Institute of Parasitology, Biology Centre, Czech Academy of Sciences, Czechia;  ² Scripps Institution of Oceanography, University of California, United States;  ³ Life Science Research Centre, University of Ostrava, Czechia;  ⁴ Faculty of Sciences, Charles University,, Czechia

Discussion

Blastocrithidia nonstop, a trypanosomatid closely related to the parasitic genera Trypanosoma and Leishmania, has reassigned all three stop codons into sense codons, yet it also uses UAA as a universal stop codon. We have sequenced, assembled and analyzed the genomes of four members of the genus Blastocrithidia and four members of the closely related genus Obscuromonas, which has a canonical genetic code. The genome-wide comparative analysis has shown that all Blastocrithidia species share the same codon reassignment and are exceptionally AT-rich, but other genomic features are remarkably similar to Obscuromonas and other trypanosomatids. In B. nonstop the in-frame UAA and UAG are decoded by tRNAs with a matched anticodon, yet UGA is decoded by a tRNA with uniquely shortened anticodon stem recognizing non-canonically both UGG and UGA codons. Corresponding tRNAs seem to be absent in Obscuromonas species. We aim to turn B. nonstop into a genetically tractable organism, which would allow addressing questions such as: Why did the massive reassignment occur in this lineage? How do in-frame stop codons influence translation? What is the role of tRNAs with short anticodon stem? Why are the in-frame stop codons more frequent in certain genes but absent in others? How does the ribosome distinguish between the in-frame and genuine UAA termination codons?