Molecular basis for coordinating transcription termination with noncoding RNA degradation

Area of Science:

• Molecular Biology
• Gene Regulation
• RNA Processing

Background:

• The Nrd1-Nab3-Sen1 (NNS) complex regulates pervasive transcription and generates small RNAs in Saccharomyces cerevisiae.
• NNS terminates noncoding RNA transcription and facilitates exosome-mediated processing and degradation.
• The Trf4-Air2-Mtr4 (TRAMP) complex polyadenylates NNS targets, promoting their degradation.

Purpose of the Study:

• To elucidate the mechanism coupling NNS-dependent transcription termination and RNA degradation.
• To investigate the structural and functional basis of NNS complex interactions with other factors.

Main Methods:

• Structural analysis of the Nrd1p protein.
• In vivo and in vitro biochemical assays.
• Functional studies in Saccharomyces cerevisiae.

Main Results:

• Identified a key domain in Nrd1p that interacts mutually exclusively with RNA polymerase II and Trf4p.
• Demonstrated that Nrd1p can exist in two alternative forms, one for termination and one for degradation.
• Showed that the Nrd1p-Trf4p interaction is crucial for exosome activity and TRAMP-mediated polyadenylation in vivo and in vitro.

Conclusions:

• The NNS complex coordinates transcription termination and RNA degradation through alternative interactions of Nrd1p.
• Switching between Nrd1p partners (RNA polymerase II vs. Trf4p) dictates the complex's function in termination or degradation.
• This dynamic mechanism ensures efficient control of noncoding RNA metabolism.