Structure of a gene coding for human HMG2 protein.

A human genomic library was screened with the pig thymus cDNA coding for chromosomal protein HMG2. A 4341-base pair fragment containing the entire gene encoding this protein was isolated and characterized. The HMG2 gene is 2665 base pairs long from the start site to the end of transcription and comprises 5 exons. The size of mRNA postulated from the exons is 1125 base pairs long, consistent with that obtained by Northern hybridization analysis. The canonical 5'-regulatory motifs, CCAAT, are present, while the TATA element is absent from the gene. Southern analysis suggested that HMG2 protein is encoded by a single or only a few genes of high homology. The primary structure of the human HMG2 protein consists of 208 amino acid residues, deduced from the coding region of the gene, is different from that of pig HMG2 in only two amino acids; one is exchanged and the other is missing. The amino acid sequences of two DNA binding domains, "HMG-box," also recently found in several transcription factors, are completely homologous in human and pig HMG2. The present study, which is the first one on the isolation and characterization of complete gene coding for HMG2 protein, may be useful for evolutional and genomic analysis of the proteins containing the HMG-box sequences for DNA binding.