A rho-independent termination caused by the cloned inverted nut L site of phage lambda.

For studying the termination activity of inverted nutL site of bacteriophage lambda, we have constructed a plasmid carrying the nutL fragment oriented reversely with respect to cloned lambda promoter p'R-directed transcription. The results of in vitro transcription on this plasmid template and S1 mapping assay reveal that the termination of p'R-promoted transcription at inverted nutL site is a rho-independent event. This nutL terminator shares several features with the other known sites of transcription termination, including (i) a uridine-rich 3' terminal RNA sequences,--UUAAUUUUU-OH, (ii) a GC-rich region in the DNA immediately preceding the site of termination, (iii) a region of dyad symmetry in the DNA which, in transcript, is capable of forming a stable hairpin containing four GC base pairs and one AU base pair in its stem.