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Crosstalk In DNA‐Alkyltransferase Functions
Author(s) -
Fried Michael,
Tessmer Ingrid
Publication year - 2015
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.29.1_supplement.490.3
Subject(s) - proliferating cell nuclear antigen , dna , chromatin , biology , dna repair , microbiology and biotechnology , cooperativity , lesion , o 6 methylguanine dna methyltransferase , dna binding protein , biophysics , chemistry , biochemistry , methylation , methyltransferase , gene , transcription factor , psychology , psychiatry
DNA alkyltransferases protect genomic integrity, but under some conditions can also defend tumor cells against chemotherapeutic alkylating agents. Here we examine mechanisms that regulate the DNA‐binding and repair activities of human O 6 ‐alkylguanine‐DNA alkyltransferase (AGT). AGT binds O 6 ‐methylG‐C and O 6 ‐methylG‐T lesions with specificity far too low for efficient lesion search. This suggests that other factors are needed to direct AGT to lesion sites. Recently we have found that AGT binds the human MutSβ homologue and PCNA proteins. In vitro , MutSβ inhibits alkyltransferase activity on short duplex DNAs, while PCNA increases repair rates on single‐stranded DNAs and long duplexes. The compositions and binding activities of MutSβ‐AGT and PCNA‐AGT complexes suggest roles for these interactions in lesion search. In addition to lesion‐specific binding, the surveillance process includes interactions with lesion‐free DNAs. The non‐specific binding of AGT is homo‐cooperative, allowing high densities to be attained in the absence of other proteins. Protein‐protein contacts that contribute to cooperativity are predicted to be optimal over a narrow range of DNA twist values. Outside of those values, torsional free energy will limit cooperative cluster size. Assays using superhelical DNAs show that binding densities and alkyltransferase rates decrease with the linking difference, ΔLk. These results predict that AGT and its DNA‐repair activities will partition in favor of torsionally‐relaxed, relatively protein‐free DNA structures like those found near sites of chromatin remodeling. This binding preference may play an important role in genome surveillance. Supported by NIH grant GM070662 to MGF.