Faculty Bibliography

In bacteria, an intrinsic transcription termination signal appears in RNA as a hairpin followed by approximately eight uridines (U stretch) at the 3' terminus. This signal leads to rapid dissociation of the ternary elongation complex (TEC) into RNA, DNA, and an RNA polymerase. We demonstrate that the hairpin inactivates and then destabilizes TEC by weakening interactions in the RNA-DNA hybrid-binding site and the RNA-binding site that hold TEC together. Formation of the hairpin is restricted to the moment when TEC reaches the point of termination and depends upon melting of four to five hybrid base pairs that follow the hairpin's stem. The U stretch-induced pausing at the point of termination is crucial, providing additional time for hairpin formation. These results explain the mechanism of termination and aid in understanding of how cellular factors modulate this process

During RNA synthesis in the ternary elongation complex, RNA polymerase enzyme holds nucleic acids in three contiguous sites: the double-stranded DNA-binding site (DBS) ahead of the transcription bubble, the RNA-DNA heteroduplex-binding site (HBS), and the RNA-binding site (RBS) upstream of HBS. Photochemical cross-linking allowed mapping of the DNA and RNA contacts to specific positions on the amino acid sequence. Unexpectedly, the same protein regions were found to participate in both DBS and RBS. Thus, DNA entry and RNA exit occur close together in the RNA polymerase molecule, suggesting that the three sites constitute a single unit. The results explain how RNA in the integrated unit RBS-HBS-DBS may stabilize the ternary complex, whereas a hairpin in RNA result in its dissociation