Cyclic CMP and cyclic UMP mediate bacterial immunity against phages

Nitzan Tal, Benjamin R. Morehouse, Adi Millman, Avigail Stokar-Avihail, Carmel Avraham, Taya Fedorenko, Erez Yirmiya, Ehud Herbst, Alexander Brandis, Tevie Mehlman, Yaara Oppenheimer-Shaanan, Alexander F.A. Keszei, Sichen Shao, Gil Amitai, Philip J. Kranzusch*, Rotem Sorek*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

96 Scopus citations


The cyclic pyrimidines 3′,5′-cyclic cytidine monophosphate (cCMP) and 3′,5′-cyclic uridine monophosphate (cUMP) have been reported in multiple organisms and cell types. As opposed to the cyclic nucleotides 3′,5′-cyclic adenosine monophosphate (cAMP) and 3′,5′-cyclic guanosine monophosphate (cGMP), which are second messenger molecules with well-established regulatory roles across all domains of life, the biological role of cyclic pyrimidines has remained unclear. Here we report that cCMP and cUMP are second messengers functioning in bacterial immunity against viruses. We discovered a family of bacterial pyrimidine cyclase enzymes that specifically synthesize cCMP and cUMP following phage infection and demonstrate that these molecules activate immune effectors that execute an antiviral response. A crystal structure of a uridylate cyclase enzyme from this family explains the molecular mechanism of selectivity for pyrimidines as cyclization substrates. Defense systems encoding pyrimidine cyclases, denoted here Pycsar (pyrimidine cyclase system for antiphage resistance), are widespread in prokaryotes. Our results assign clear biological function to cCMP and cUMP as immunity signaling molecules in bacteria.

Original languageAmerican English
Pages (from-to)5728-5739.e16
Issue number23
StatePublished - 11 Nov 2021
Externally publishedYes

Bibliographical note

Publisher Copyright:
© 2021 Elsevier Inc.


  • Pycsar
  • anti-phage
  • bacteria
  • cCMP
  • cUMP
  • cyclase
  • defense
  • pb8
  • phage
  • pyrimidine


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