The central region of c-Myc protein between amino acids 143 and 352 is
involved in interaction with Sp1. (A) The structural
domains of c-Myc and the c-Myc mutants used in this work are
diagrammed. Domains include the transcriptional activation domain
(TAD), a basic region (B), a helix–loop–helix motif (HLH), and
leucine zipper domain (LZ). (B) 293 cells were
transfected with expression constructs for T7-tagged c-Myc, the Myc
deletion mutants MycΔ7–91, MycΔ106–143, and MycΔ352–439, and
the Myc fragment 250–352 and harvested 48 h after transfection.
Pull-down assays were performed by incubating lysates with GST or
GST-Sp1-(612–778) for 1 h at 4°C followed by incubation with
glutathione beads for 1 h. Bound proteins were subjected to
SDS/PAGE followed by immunoblotting with anti-T7 antibody.