Available online 5 March 2024

Transcription of spliceosomal small nuclear RNAs (snRNAs) in Trichomonas vaginalis bypasses conventional capping.

Spliceosomal snRNAs of T. vaginalis have 5’-triphosphate ends.

Spliceosomal snRNAs of T. vaginalis lack standard core promoter elements.

The U6 snRNA of T. vaginalis dispenses with the TATA box for transcription and RNA polymerase selectivity.

U6 snRNA transcription in T. vaginalis is insensitive to tagetitoxin.

Trichomonas vaginalis is a medically important protozoan parasite, and a deep-branching, evolutionarily divergent unicellular eukaryote that has conserved several key features of eukaryotic gene expression. Trichomonas vaginalis possesses a metazoan/plant-like capping apparatus, mRNAs with a cap 1 structure and spliceosomes containing the five small nuclear RNAs (snRNAs). However, in contrast to metazoan and plant snRNAs, the structurally conserved T. vaginalis snRNAs were initially identified as lacking the canonical guanosine cap nucleotide. To explain this unusual condition, we sought to investigate transcriptional and processing features of the spliceosomal snRNAs in this protist. Here, we show that T. vaginalis spliceosomal snRNA genes mostly lack typical eukaryotic promoters. In contrast to other eukaryotes, the putative TATA box in the T. vaginalis U6 snRNA gene was found to be dispensable for transcription or RNA polymerase selectivity. Moreover, U6 transcription in T. vaginalis was virtually insensitive to tagetitoxin compared with other cellular transcripts produced by the same RNA polymerase III. Most important and unexpected, snRNA transcription in T. vaginalis appears to bypass capping as we show that these transcripts retain their original 5’-triphosphate groups. In conclusion, transcription and processing of spliceosomal snRNAs in T. vaginalis deviate considerably from the conventional rules of other eukaryotes.

Small nuclear RNAs

Spliceosomal snRNAs

Capping

Guanosine cap

Divergent eukaryote

Protozoan parasite

© 2024 The Authors. Published by Elsevier Ltd on behalf of Australian Society for Parasitology.