Nuclear protein factor binds specifically to the 3'-regulatory module of the long-interspersed-nuclear-element-like Dictyostelium repetitive element

The Dictyostelium repetitive element DRE integrates in a position-specific manner upstream of tRNA genes in the Dictyostelium discoideum genome. DRE has structural similarities to the group of long interspersed nuclear elements. whose replication mechanism is poorly understood. The C-module at the 3' end of DRE encodes a regulatory cis-acting sequence that contains an RNA polymerase II promoter. This promoter directs the synthesis of RNAs that are thought to play a critical role in DRE transposition. In this study, we describe the identification of a nuclear protein factor that binds to the C-module in a sequence-specific manner. The C-module-binding factor (CMBF) recognizes three DNA sequence motifs that contain homopolymeric (dT) stretches of variable lengths, but does not bind to a standard RNA polymerase II promoter from D. discoideum. Analysis of highly CMBF-enriched fractions and glycerol gradient sedimentation of CMBF suggest that the factor exists as a monomeric 115-kDa protein. Possible cb roles of CMBF in DRE transposition are discussed.