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14 Escherichia coli Rho Factor: Protein and Enzyme of Transcription Termination

Terry Platt, John P. Richardson


E. coli rho factor is an essential hexameric protein of identical 47-kD subunits that is required to mediate transcription termination at various genomic and bacteriophage sites. Rho-dependent terminators have an upstream RNA component that serves as the initial recognition sequence for rho binding and another component that slows RNA chain elongation when polymerase is near the 3′ endpoints. Each rho subunit has separate domains for binding RNA and ATP. Coordinated rounds of ATP hydrolysis require RNA binding and are in turn coupled to rho translocation along the RNA toward its 3′ end. The RNA-DNA hybrid helicase activity of rho presumably facilitates termination of transcription by dissociating the RNA from its complex with the DNA template and RNA polymerase.

The importance of events that govern the specificity and efficiency of producing mature mRNA transcripts is well established, and recognition of signals controlling termination of transcription by RNA polymerase plays a crucial role in these events (Platt 1986; Yager and von Hippel 1987; Richardson 1990). Unlike the situation in eukaryotes, the 3′ ends of prokaryotic mRNAs most likely are formed as direct results of transcription termination by RNA polymerase; in some cases, RNA processing events are also involved, but they appear to play only secondary roles. E. coli RNA polymerase displays “intrinsic” transcription termination activity just downstream from sites that correspond in the RNA itself to hairpin structures followed by a stretch of uridine residues. Other aspects of structure, not yet well understood, can affect termination efficiency at such sites...

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