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Mol Cell. 1997 Dec;1(1):79-87.

Domain interactions in E. coli SRP: stabilization of M domain by RNA is required for effective signal sequence modulation of NG domain.

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Molecular Biophysics Program, University of Texas Southwestern Medical Center at Dallas 75235, USA.


The E. coli protein, Fth, binds to 4.5S RNA through its M domain to form the signal recognition particle (SRP). The other domain of Fth (NG) is a GTPase, which binds and is coordinately regulated by its receptor, FtsY. We find that the helical M domain is inherently flexible. Binding of 4.5S RNA to Fth stabilizes the M domain yet has little apparent effect on the binding of signal peptides. However, in the absence of the RNA, signal peptide binding results in a global destabilization of Fth, which is prevented by binding of 4.5S RNA. Signal peptide binding to isolated NG domain also causes a pronounced destabilization, implicating the NG domain in direct recognition of signal peptide.

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