![]() Unauthorized attempts to upload information and/or change information on any portion of this site are strictly prohibited and are subject to prosecution under the Computer Fraud and Abuse Act of 1986 and the National Information Infrastructure Protection Act of 1996 (see Title 18 U.S.C. For security purposes, and to ensure that the public service remains available to users, this government computer system employs programs to monitor network traffic to identify unauthorized attempts to upload or change information or to otherwise cause damage, including attempts to deny service to users. More Information Internet Security Policyīy using this site, you are agreeing to security monitoring and auditing. For more information, contact more information, please see the SEC’s Web Site Privacy and Security Policy. You can also sign up for email updates on the SEC open data program, including best practices that make it more efficient to download data, and SEC.gov enhancements that may impact scripted downloading processes. Please declare your traffic by updating your user agent to include company specific information.įor best practices on efficiently downloading information from SEC.gov, including the latest EDGAR filings, visit sec.gov/developer. Your request has been identified as part of a network of automated tools outside of the acceptable policy and will be managed until action is taken to declare your traffic. To allow for equitable access to all users, SEC reserves the right to limit requests originating from undeclared automated tools. For example, the use of standard B-DNA geometry for the operator is clearly an approximation.Your Request Originates from an Undeclared Automated Tool The current models for the complexes of Cro, repressor, and CAP with operator DNA are probably fundamentally correct, but it should be emphasized that model building alone, even when coupled with genetic and biochemical studies, cannot be expected to provide a completely reliable "high-resolution" view of the protein-DNA complex. These specific interactions, together with backbone interactions and electrostatic interactions, stabilize the protein-DNA complexes. Recognition of specific base sequences involves hydrogen bonds and van der Waals interactions between side chains and the edges of base pairs. However, lambda repressor contacts both sides of the double helix by using a flexible region of protein to wrap around the DNA. Most of the contacts made by Cro, repressor, and CAP occur on one side of the double helix. This use of alpha-helical regions for DNA binding appears to be a common mode of recognition. An adjacent alpha-helical region contacts the DNA backbone and may help to orient the "recognition" helices. Cro, repressor, and CAP use alpha-helices for many of the contacts between side chains and bases in the major groove. Some sequence-specific DNA-binding proteins, like RNA polymerase, do not have symmetrically related subunits and do not bind to symmetric recognition sequences. However, there is no requirement for symmetry in protein-DNA interactions. It seems likely that these proteins will, like Cro, repressor, and CAP, form symmetric complexes. Many other DNA-binding proteins are dimers or tetramers and their operator sequences have approximate two-fold symmetry. Cro, repressor, and CAP use symmetrically related subunits to interact with two-fold related sites in the operator sequences. There seem to be proteins that bind left-handed Z-DNA (87) and DNA in other conformations, but it remains to be seen how these structures are recognized or how proteins recognize specific sequences in single-stranded DNA. They do not form cruciforms or other novel DNA structures. The DNA-binding sites are recognized in a form similar to B-DNA. Several general principles emerge from the studies of Cro, lambda repressor, and CAP.
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