INVOLVEMENT OF ANTISENSE RNA IN REPLICATION CONTROL OF THE LACTOCOCCAL PLASMID PND324

pND324 belongs to a family of closely related theta-type plasmids from Lactococcus lactis. An antisense RNA, termed countertranscript (ctRNA ), was identified which is complementary to the leader sequence of the mRNA that encodes RepB, a protein essential for plasmid replication. When the synthesis of ctRNA was abolished by site-directed mutagenesis within its promoter region, the mutant replicon showed a 1.8-fold inc rease in copy number. Similar ctRNA promoter sequences are readily ide ntifiable in 12 other published lactococcal theta-type plasmids, sugge sting that they all encode a similar ctRNA-mediated regulatory mechani sm. (C) 1998 Published by Elsevier Science B.V. All rights reserved.