Kid cleaves specific mRNAs at UUACU sites to rescue the copy number of plasmid R1

Abstract

Stability and copy number of extra‐chromosomal elements are tightly regulated in prokaryotes and eukaryotes. Toxin Kid and antitoxin Kis are the components of the parD stability system of prokaryotic plasmid R1 and they can also function in eukaryotes. In bacteria, Kid was thought to become active only in cells that lose plasmid R1 and to cleave exclusively host mRNAs at UA(A/C/U) trinucleotide sites to eliminate plasmid‐free cells. Instead, we demonstrate here that Kid becomes active in plasmid‐containing cells when plasmid copy number decreases, cleaving not only host‐ but also a specific plasmid‐encoded mRNA at the longer and more specific target sequence UUACU. This specific cleavage by Kid inhibits bacterial growth and, at the same time, helps to restore the plasmid copy number. Kid targets a plasmid RNA that encodes a repressor of the synthesis of an R1 replication protein, resulting in increased plasmid DNA replication. This mechanism resembles that employed by some human herpesviruses to regulate viral amplification during infection.

Bacterial addiction module toxin Doc inhibits translation elongation through its association with the 30S ribosomal subunit

“…Doc Expression Leads to mRNA Stabilization. Some TA toxins lead to translation arrest indirectly by elimination of virtually all of the intracellular mRNA through their sequence-specific endoribonuclease activity [e.g., E. coli MazF (27) and ChpBK (28), Kid on plasmid R1 (29), and PemK on plasmid R100 (30)]. We analyzed the effect of Doc expression on the steady-state levels of mRNA in vivo.…”

Toxin Kid uncouples DNA replication and cell division to enforce retention of plasmid R1 in Escherichia coli cells

“…We also found that Kid cleaved mRNA at UUACU sites, which appeared well suited to trigger a response that prevented plasmid loss and increased R1 CNs without killing cells, as suggested by our results. In view of all this, we argued that Kid and Kis functioned as a rescue system for plasmid R1, and not as a PSK system (24). This proposal cannot be supported by results elsewhere, suggesting that Kid may cleave mRNA at simpler UAH sites (with H being A, C, or U) (25,26), a view that has prevailed in the literature (14,16,(27)(28)(29).…”

“…Thus, overexpression of copA, an antisense RNA that impedes translation of repA, reduces R1 content in host cells as they divide and leads to the eventual production of plasmid-free descendants in the population (33). Two observations made when we used this strategy in E. coli cells carrying an R1 derivative bearing kis-kid argued against a PSK function for this TA pair (24). First, activation of Kid occurred in cells that still contained the plasmid; second, this inhibited growth of our cultures but did not kill cells, because they resumed proliferation when further expression of copA was discontinued.…”

“…These observations explained why activation of Kid in our mR1KK samples was not paralleled by a decrease in OD 600 relative to control samples at early time points. Moreover, although Kid cleaves mRNA and inhibits protein synthesis (24)(25)(26), the cell enlargement shown in Fig. 2A suggested that the toxin does not halt protein production completely in E. coli.…”

Targeted cell‐ablation in Xenopus embryos using the conditional, toxic viral protein M2(H37A)

“…Unfortunately, DTR-mediated cell-ablation methods are currently limited to rodents and it is unclear if they work with developing embryos. A third controllable, cell death technology is the endoribonuclease Kid toxin (de la Cueva-Mendez et al, 2003;Pimentel et al, 2005; Fig. 2K-M, Supplementary Movie S3).…”