Functional analysis of the Enterococcus faecalis plasmid pAD1‐encoded stability determinant par

Summary The molecular organization and functional characteristics of the pAD1 replicon‐encoded par stability determinant were examined, par encodes two convergently transcribed RNAs of 210 and 65 nucleotides designated RNA I and RNA II, respectively. The sequence of RNA II is largely complementary to RNA I, suggesting that RNA II could regulate RNA I function as an anti‐sense RNA. Results of functional studies are consistent with a role for par as a post‐segregational killing system, the first to be identified in Gram‐positive bacteria, with RNA I encoding the toxin and RNA II the antidote. These results include: (i) destabilization of par‐containing replicons in the presence of a second complete par or the RNA II coding sequence in the same cell; (ii) par‐dependent stabilization of a highly unstable vector at the expense of host‐cell growth rate; and (iii) protection of cells from the toxic effects of overexpression of RNA I by RNA II supplied in trans.