Selection of homeotic proteins for binding to a human DNA replication origin

We have previously shown that a cell cycle-dependent nucleoprotein complex assembles in vivo on a 74 bp sequence within the human DNA replication orig in associated to the Lamin B2 gene. Here, we report the identification, usi ng a one-hybrid screen in yeast, of three proteins interacting with the 74 bp sequence. All of them, namely HOXA13, HOXC10 and HOXC13, are orthologues of the Abdominal-B gene of Drosophila melanogaster and are members of the homeogene family of developmental regulators. We describe the complete open reading frame sequence of HOXC10 and HOXC13 along with the structure of th e HoxC13 gene. The specificity of binding of these two proteins to the Lami n B2 origin is confirmed by both band-shift and in vitro footprinting assay s. In addition, the ability of HOXC10 and HOXC13 to increase the activity o f a promoter containing the 74 by sequence, as assayed by CAT-assay experim ents, demonstrates a direct interaction of these homeoproteins with the ori gin sequence in mammalian cells. We also show that HOXC10 expression is cel l-type-dependent and positively correlates with cell proliferation. (C) 200 0 Academic Press.