A Nuclear Protein factor Binds Specifically to the 3′‐Regulatory Module of the Long‐Interspersed‐Nuclear‐Element‐Like Dictyostelium Repetitive Element

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Abstract
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 roles of CMBF in DRE transposition are discussed.