Category Archives: Events

Ivan (Vanya) Zheludev’s Ph.D. Thesis Defense: “Obelisks”

• Tuesday, July 9, 2024
• 10 am – 11 am PST
• Munzer Auditorium (Beckman Center Ground Floor Room B060)

Manuscript abstract: Here, we describe “Obelisks,” a previously-unrecognised class of viroid-like elements found in metatranscriptomic datasets. Obelisks share several properties: (i) apparently circular RNA ~1kb genome assemblies, (ii) predicted rod-like genome-wide secondary structures, and (iii) open reading frames encoding a novel “Oblin” protein superfamily. A subset of Obelisks additionally include an Obelisk-specific variants of the hammerhead self-cleaving ribozyme. Obelisks form their own phylogenetic group without detectable similarity to known biological agents. Surveying globally, we identify 29,959 distinct Obelisks (clustered at 90% sequence identity) from diverse ecological niches. Obelisks are prevalent in human microbiomes, with detection in ~7% (29/440) and ~50% (17/32) of queried stool and oral metatranscriptomes, respectively. We establish Streptococcus sanguinis as a cellular host of a specific Obelisk, and find that this Obelisk’s maintenance is not essential for bacterial growth. As such, these observations identify Obelisks as a class of diverse RNAs of cryptic impact that have colonised, and gone unnoticed in, human, and global microbiomes.

To request the Zoom link, please email Dan Carino (dpcarino@stanford.edu)