Trends in Microbiology
Volume 28, Issue 4, April 2020, Pages 293-303
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Review
The Cap-Snatching Mechanism of Bunyaviruses

https://doi.org/10.1016/j.tim.2019.12.006Get rights and content
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Highlights

  • Endonuclease domains have been located in many different bunyavirus L proteins and can be classified as His+ or His– metal-dependent endonucleases.

  • An active cap-binding domain (CBD) has been identified in the C-terminal region of bunyavirus L protein. Despite very low sequence identity, this domain is very similar to influenza virus PB2 CBD on the structural level.

  • Atomic structures of bunyavirus N protein do not provide evidence for the hypothesized N protein cap-binding site. It remains unclear whether a functionally relevant cap-specific binding site exists in any bunyavirus N protein.

  • The comparably low affinity of bunyavirus CBD for cap-structures indicates the necessity for further regions of the L protein or other viral or cellular proteins to be involved in cap binding.

In common with all segmented negative-sense RNA viruses, bunyavirus transcripts contain heterologous sequences at their 5′ termini originating from capped host cell RNAs. These heterologous sequences are acquired by a so-called cap-snatching mechanism. Whereas for nuclear replicating influenza virus the source of capped primers as well as the cap-binding and endonuclease activities of the viral polymerase needed for cap snatching have been functionally and structurally well characterized, our knowledge on the expected counterparts of cytoplasmic replicating bunyaviruses is still limited and controversial. This review focuses on the cap-snatching mechanism of bunyaviruses in the light of recent structural and functional data.

Keywords

bunyavirus
cap snatching
viral transcription
endonuclease
cap binding

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