Arbitrium systems control lysis/lysogeny through the regulation of small antirepressor proteins

Many temperate Bacillus phages utilize the arbitrium signaling system to control lysis/lysogeny decisions. While the function of the arbitrium signal AimP and its receptor AimR are well known, it is unclear how they control lysis in most arbitrium systems. Here, we show that a large majority of arbitrium systems are embedded in an extended module with three additional components; A small antirepressor protein (AimX), the phage repressor (AimC) and an adjacent cro-like protein (AimL). AimR-dependent activation of AimX is necessary for lysis both during infection and lytic induction. Molecular analysis suggests that AimX directly binds AimC and prevents its oligomerization and binding to its regulated aimL promoter. Our work therefore uncovers the main mechanism by which arbitrium systems regulate lysis and point to the central role of small proteins in phage decision making. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=176 SRC="FIGDIR/small/689978v1_ufig1.gif" ALT="Figure 1"> View larger version (35K): org.highwire.dtl.DTLVardef@63dd49org.highwire.dtl.DTLVardef@54e7ecorg.highwire.dtl.DTLVardef@466235org.highwire.dtl.DTLVardef@d98ef2_HPS_FORMAT_FIGEXP M_FIG C_FIG