Fig. 3

Extracellular XseB in-situ tailors poly(dC) at 5′ terminus. a Assays for the single strand-specific 5′ → 3′ cleavage activity of XseB. A Cy5 fluorescent label was attached to 5′ terminus of ssDNA with a hairpin structure in its 3′ terminus (5′-*poly(dC₂₀)AAAAAACCTTTTTT-3′) or was attached to 5′ terminus of dsDNA (5′-*GTCATTCTGAGAATAGTGTAG-3′). The recombinant XseB resulted in the disappearance of fluorescence in free and RmlB-bound ssDNA rather than dsDNA. b Persistence in (s) WT cells plus recombinant XseB. The XseB-treated (s) WT cells exhibited the same persister level as that in (d) WT cells. c Persistence in (s) WT cells that was resuspended in the final filtrate plus His-tagged XseA or in the XseB-free final filtrate. Both the final filtrate and the His-tagged XseA treated final filtrate increased persistence in (s) WT cells. But the XseB-free final filtrate failed to increase persistence in (s) WT cells. d Persistence in cells expressing xseB_asRNA. Plasmid pBBR1MCS3a-X2 had a xseB_asRNA expression cassette. Expression of xseB_asRNA with 0.2% l-arabinose induction caused the loss of persistence enhancement in the (d) cells. As a control, the stimulation in persistence was still present in the (d) cells harboring pBBR1MCS3a-X2 without l-arabinose induction. Washing increased persistence in the (s) cells harboring pBBR1MCS3a-X2 no matter with or without l-arabinose induction. All experiments were performed in biological triplicates. Error bars represent standard deviations. Dot plots overlaid on bar graphs represent individual data points. Black spot, treatment step or object; arrow, treatment order; hash sign, inactivated protein