Functional domains involved in the interaction between Orc1 and transcriptional repressor AlF-C that bind to an origin/promoter of the rat aldolase B gene

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Abstract
The promoter of the rat aldolase B (AldB) gene functions in vivo as an origin of DNA replication in the cells in which transcription of the gene is repressed. Previously, we identified two closely related DNA‐binding proteins, AlF‐C1 and AlF‐C2, which repressed the AldB gene promoter. We also reported that the binding site of these proteins, site C, is one of the required DNA elements of the AldB gene origin/promoter for autonomously replicating activity in transfected cells. In the present study, we show that AlF‐C1 and AlF‐C2 bind directly to Orc1, a subunit of the origin recognition complex (ORC). Deletion analyses revealed a functional domain in AlF‐C2 for binding to Orc1, which is located separately from the DNA‐binding domain. In addition, we found a novel protein‐interacting domain in Orc1 required for the binding of AlF‐C2, which was conserved in human, mouse and Chinese hamster, but not in Drosophila, frog and yeast. Thus, it is assumed that in mammalian cells, sequence‐ specific DNA‐binding proteins are involved in recruiting ORC to regulate replication initiation and/or transcription repression.