title: Detailed analysis of the basic domain of the E2F1 transcription factor indicates that it is unique among bHLH proteins.
abstract: The E2F1 transcription factor binds to sites within the promoters of a number of cell cycle regulated genes through a basic-helix-loop-helix motif (bHLH). It is shown here that the basic region of E2F1 is distinct from that of all other bHLH proteins. The center of the basic region contains a helix breaking proline-glycine pair, (P122, G123), implying a turn within this region. This is in contrast to the known bHLH containing proteins where the basic region is alpha-helical. Substitution of P122 and G123 with alanines results in a significant reduction in DNA binding levels, with the predicted formation of an alpha-helix. Also in contrast to other bHLH proteins, mutations generated in conserved basic residues of E2F1 do not effect DNA binding. In addition, a single leucine (191) between helix no. 2 and the leucine zipper is required for DNA binding while the leucine zipper itself is not necessary. Finally, E2F1 interacts with all of the G-residues in the sequence GGCGGGAAA while the A-residues are not required for DNA binding. The uniqueness of the E2F1 DNA binding domain is likely to play a role in its binding a DNA site that is distinct from that of all other bHLH proteins (CACGTG).
authors.affiliation: Department of Biochemistry and Molecular Biology, Thomas Jefferson University, Philadelphia, PA 19107.
authors.forename: K L
authors.initials: KL
authors.lastname: Jordan
authors.forename: A R
authors.initials: AR
authors.lastname: Haas
authors.forename: T J
authors.initials: TJ
authors.lastname: Logan
authors.forename: D J
authors.initials: DJ
authors.lastname: Hall
mesh_terms: D001483:Base Sequence; D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D004247:DNA / Q000378:metabolism; D004268:DNA-Binding Proteins; D050684:E2F Transcription Factors; D050687:E2F1 Transcription Factor; D004586:Electrophoresis; D005998:Glycine / Q000032:analysis; D008745:Methylation; D008969:Molecular Sequence Data; D017354:Point Mutation; D011392:Proline / Q000032:analysis; D011487:Protein Conformation; D056465:Retinoblastoma-Binding Protein 1; D014157:Transcription Factors / Q000737:chemistry*
chemical_list: D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; D050684:E2F Transcription Factors; D050687:E2F1 Transcription Factor; D056465:Retinoblastoma-Binding Protein 1; D014157:Transcription Factors; D004247:DNA; D011392:Proline; D005998:Glycine