Characterization of the chicken and rat DCoH gene domains using an improved ligation-mediated PCR method.

The bifunctional protein DCoH (dimerization cofactor of HNF-1) is a transcriptional coactivator of homeodomain proteins and a cytoplasmic enzyme. Here we report on the isolation, nucleotide sequence and genomic structure of the chicken and rat DCoH genes. They have an unusual first exon coding for a single amino acid. The promoters are located within CpG-islands and lack TATA and CAAT consensus sequences. Analysis of the number of CpG dinucleotides in the promoter indicates little changes since man and chicken were separated in evolution whereas a 67% reduction was observed in the rat lineage. The DNA sequences were obtained entirely without cloning. For walking into unknown genomic regions we describe a modification of the ligation-mediated polymerase chain reaction (LM-PCR) that can replace conventional screening and cloning methods and greatly expedite the isolation of genomic DNA.