Fig. 5: HNH nuclease degrades E. coli tRNASer.
From: Structural basis of antiphage defence by an ATPase-associated reverse transcriptase
a Fluorescence microscopy images for WT or HNH-inactive (H71A) retron in the presence of T3 exonuclease. Cell membrane is labeled with WGR Oregon (violet). DNA is labeled with DAPI (blue). Arrows indicate cells with DNA compacted away from the cell membrane. Images representative of n = 2 independent biological replicates. b Volcano plot comparing tRNA abundance between cells expressing WT retron and T3 exonuclease versus those expressing an HNH-inactive retron and exonuclease. The p value is calculated using a two-sided negative binomial test. Data shown is representative of n = 3 independent biological replicates. c WT T5 sequence with the deleted region in T5MSU highlighted in cyan. The location of the phage tRNASer are indicated. d Proposed model for antiphage defence by the ATPase-associated RT. The RT reverse-transcribes a ncRNA into an extrachromosomal DNA that recruits SMC ATPases. The HNH toxin is recruited. Upon infection, phage flap nuclease degrades the msDNA, potentially releasing the HNH, which depletes E. coli tRNASer. The flap nuclease from T7 degrades msDNA, but T7 is resistant to type I-A retron mediated defense, suggesting a virally encoded anti-retron.
