NLM DIR Seminar Schedule

Abstract:

Covalently closed circular RNAs (cccRNA) are known to be generated in all forms of life and are involved in various cellular processes and even linked to cancer. Further, they are the genomic template for independent replicators such as viroids and viroid-like elements such as Ribozyviria (including Hepatitis Delta Virus, HDV), virusoids, ambiviruses and a recently discovered group called Obelisks. These Obelisks are about 1 kb long, encode for at least one protein called Oblin-1 and are found to replicate in bacteria.

Although the existence of viroids has been known for more than 50 years, many aspects of cccRNA replicators are far from being understood, including their variety, host cells and whether other unrelated groups exist.

Here, I will present our results characterizing nearly 13 million putative cccRNAs found in (meta)transcriptomic data and how they can help us to understand the abundance of cccRNA replicators better. The main focus will be on the identification of novel Obelisks. By combining protein sequence and structure-based searches, we were able to identify thousands of very diverse Obelisk replicators. The discovered Obelisks were found in samples from very different environments, indicating a broad host diversity. A large CRISPR spacer search links several of the identified Obelisks to diverse bacterial hosts, mainly associated with gut environments. These findings highlight that Obelisks are widespread but until now overlooked components of microbial ecosystems and expand our understanding of viroid-like cccRNA replicator diversity and evolution. Further, I will show preliminary results on additional independent and distinguishable potential cccRNA replicators.