MODULATION OF DNA TOPOLOGY BY FLAR, A NEW GENE FROM LISTERIA-MONOCYTOGENES

We report the identification of a previously unknown Listeria monocyto genes gene, flaR, which modulates DNA topology. Through the analysis o f a Tn917 non-motile mutant, LOSC1, in which production of flagellin w as abolished, we have identified a bacterial component involved in gen e regulation. The transposon had inserted in flag an open reading fram e of 531 bp, followed by a second open reading frame of 1252 bp in rev erse orientation. On the L. monocytogenes physical map, flaR was locat ed in a different region from that of the flaA gene encoding flagellin . Transcriptional analysis showed that the flaR gene product affects t he flaA expression and negatively regulates its own expression. When e xpressed in Escherichia coli, flaR encodes a protein of 18 kDa (FlaR) whose transcription is osmoregulated. In addition, FlaR also influence s the expression of reporter genes containing supercoiling-sensitive p romoters such as proU or ompC. The data presented here suggest that Fl aR is a histone-like bacterial protein which acts at specific sites to influence DNA topology and, therefore, transcription. flaR is the fir st gene of this class to be described in Gram-positive pathogenic bact eria.