Effect of the promoter structure on the nutL transcription antitermination function

Several boxA-less 74-bp nutL antiterminator fragments do not function as antiterminators of plac-promoted transcription, but are active with the pp and p'R promoters at 30 degrees C. At elevated temperatures (42 degrees C), these defective 74-bp nutL modules retain 50% of their activity when controlled by the p'R promoter; with the pp promoter the antitermination activity is 5-10 times less efficient. Similarly, deletions of 1-3 bp in the spacer region between the boxA and boxB subunits of nutL (which abolish antitermination promoted by plac), allow rather efficient but thermosensitive antitermination when controlled by the pp or p'R promoter. These results point to possible conditional interactions between the promoter and antiterminator elements and functions. Also noted were unexpectedly slow mobilities of the p'R-nutL-bearing fragments, suggesting some unusual secondary structures.