HUMAN CART1, A PAIRED-CLASS HOMEODOMAIN PROTEIN, ACTIVITIES TRANSCRIPTION THROUGH PALINDROMIC BINDING-SITES

Homeodomain proteins play important roles in animal development by con trolling the expression of genes involved in determining cell fates. T he recently cloned human Cart1 gene encodes a paired-class homeodomain (hCART1), whose rodent homolog is mainly expressed in early chondrocy tes and in prechondrocytic mesenchymal cells. To better understand its role as a transcription factor, the author has selected specific hCAR T1 binding sites from a random pool of oligonucleotides. It is reporte d here that all sites obtained contain a palindrome consisting of two TAAT sequences separated by three or four base pairs. In electromobili ty shift assays, recombinant hCART1 proteins bind to a palindromic pro be as a multimer, possibly a homodimer. In transient transfection assa ys, hCART1 activates transcription from reporter plasmids containing h CART1 binding sites in HeLa cells, demonstrating both site dependence and dosage-dependence. It is also shown here that hCART1 localizes to nucleus. These data indicate that hCART1 is a sequence-specific transc ription activator in HeLa cells. In combination with data from previou s studies in which hCART1 represses transcription in different cell ty pes and promoters, they suggest that hCART1 may be a transcription mod ulator with both repression and activation activities. (C) 1998 Academ ic Press.