Ravi Kumar, Baylor College of Medicine

Ravi Kumar1, Neetu, Neetu1, Dilip Kumar1, Sue E Crawford2, Mary K Estes2, and B. V. Venkataram Prasad1,2 1The Verna and Marrs McLean Department of Biochemistry and Molecular Pharmacology, 2Department of Molecular Virology and Microbiology, Baylor College of Medicine, Houston, TX, USA. Corresponding author: BVV Prasad, e-mail: vprasad@bcm.edu

Among the ten rotavirus (RV) groups (A–J), group A RVs (RVAs), and, to a lesser extent, group C RVs (RVCs) are the causative agents of life-threatening gastroenteritis in children worldwide. Capping of the nascent transcripts during endogenous transcription is a critical first step in RV replication and essential for efficient translation. VP1, the viral RNA polymerase, and VP3, the capping enzyme within the intact double-layered particles, orchestrate this process. Unlike VP3A, VP3 of other RV groups is less well characterized. Sequence comparisons of VP3 show that the C-terminal PDE domain of VP3A implicated in binding to the RNA and RNA-triphosphatase (RTPase) activity is present only in VP3 of RVA, RVB, and RVG and absent in other VP3s, including RVC (VP3C). Here, our biochemical characterization of the recombinant VP3C shows several interesting differences from VP3A. Unlike the tetrameric VP3A, VP3C forms a dimer. Despite lacking the PDE domain, VP3C carries out all essential capping activities, including RTPase, guanylyl transferase (GTase), and two methyltransferase functions required for mRNA capping. Our data suggests 1) that in VP3C, the GTase domain binds the RNA and performs RTPase activity, and 2) that in VP3A the PDE domain is likely redundant during endogenous transcription and its GTase domain performs the RTPase activity. Ongoing high-resolution structural and mutational analysis will provide a better understanding of how VP3C and VP3A differ in their RNA capping mechanisms. Supported by NIAID grant AI36040 (to BVVP).