Nucleic Acids Research, 1992, Vol. 20, No. 2 337-341
© 1992
MOLECULAR BIOLOGY |
The NH2-terminal arms of trp repressor participate in repressor/operator association
Department of Biological Sciences, Stanford University Stanford, CA 95403-5020, USA
*To whom correspondence should be addressed
Received August 19, 1991. Revised December 25, 1991. Accepted December 25, 1991.
The 3-dimensionaI structures of the trp represser, aporepressor, and repressor/operator complex have been described. The NH2-terminal arms of the protein, comprising approximately 12–14 residues, were not well resolved in any of these structures. Previous studies by Carey showed that the arms are required for full in vitro repressor activity. To examine the roles of the arms more fully we have removed codons 2–5 and 2–8 of the trpR gene and analyzed the resulting truncated repressers in vivo and in vitro. The 
2–5 trp represser was found to be approximately 25% as active as the wild type represser in vivo. In in vitro equilibrium binding experiments, the 2–5 trp represser was shown to be five-fold less active on operator binding. The rate of dissociation of the complex formed between the 2–5 trp represser and operator was essentially the same as the rate of dissociation of the wild type trp repressor/operator complex, However association of the 2–5 trp represser with operator was clearly defective. Since the NH2-terminal arms of the trp repressor appear to affect association predominantly they may play a role in facilitating non-specific association of repressor with DNA as represser seeks its cognate operators. The 2–8 trp repressor was unstable in vivo and in vitro, suggesting that some portion of the NH2-terminal arm is required for proper folding of the remainder of the molecule.