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Published February 16, 2020 | Supplemental Material
Journal Article Open

Genome-wide DNA sampling by Ago nuclease from the cyanobacterium Synechococcus elongatus

Abstract

Members of the conserved Argonaute (Ago) protein family provide defense against invading nucleic acids in eukaryotes in the process of RNA interference. Many prokaryotes also contain Ago proteins that are predicted to be active nucleases, however, their functional activities in host cells remain poorly understood. Here, we characterize the in vitro and in vivo properties of the SeAgo protein from the mesophilic cyanobacterium Synechococcus elongatus. We show that SeAgo is a DNA-guided nuclease preferentially acting on single-stranded DNA targets, with nonspecific guide-independent activity observed for double-stranded substrates. The SeAgo gene is steadily expressed in S. elongatus, however, its deletion or overexpression does not change the kinetics of cell growth. When purified from its host cells or from heterologous E. coli, SeAgo is loaded with small guide DNAs whose formation depends on the endonuclease activity of the argonaute protein. SeAgo co-purifies with SSB proteins suggesting that they may also be involved in DNA processing. The SeAgo-associated small DNAs are derived from diverse genomic locations, with certain enrichment for the proposed sites of chromosomal replication initiation and termination, but show no preference for an endogenous plasmid. Therefore, promiscuous genome sampling by SeAgo does not have great effects on cell physiology and plasmid maintenance.

Additional Information

© 2020 Informa UK Limited. Received 15 Aug 2019, Accepted 12 Jan 2020, Accepted author version posted online: 03 Feb 2020, Published online: 16 Feb 2020. We thank Denis Yudin for helpful discussions. This work was supported by the Russian Science Foundation [16-14-10377]; Russian Foundation for Basic Research [18-29-07086]. No potential conflicts of interest were disclosed.

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