Existence of a Transcription Factor for the Human HMG2 Gene Positively Related to the Level of HMG2 mRNA in the Cells

A functional gene encoding high mobility group 2 (HMG2) protein, which is an abundant eukaryotic DNA-binding protein, has been isolated. The expression of the HMG2 gene is enhanced in exponentially growing cells and in cells transformed with various viral genes and oncogenes. We attempted to identify and characterize the HMG2 gene structure and transcription factor(s) participating in the expression of the gene. Chloramphenicol acetyltransferase assays to characterize the 5'-flanking region of the human HMG2 gene revealed that the nucleotide sequences in two regions are necessary for expression of the HMG2 gene: one (-85 to +44 region) as a core promoter, and the other (-621 to -493 region) as a cis regulatory element(s). Electrophoresis mobility shift assay with a DNA fragment containing the cis regulatory element and a crude nuclear extract from HeLa cells gave several complexes. Chemical footprint and competition assays indicated that the component giving one of the major complexes recognizes a nucleotide sequence of -499 to -486 in the cis regulatory element. Chloramphenicol acetyltransferase assay indicated that the component giving the major complex is required for the effective transcription of the HMG2 gene. The binding component named HMG2TF (HMG2 transcription factor) contained a protein in apparent molecular size of 85,000, as determined by a UV cross-linking experiment. The amount of HMG2TF in the growing cells and transformed cells increased in positive relationship to the level of expression of HMG2 mRNA in the cells. These results suggest that HMG2 gene expression may be regulated by the relative amount of this transcription factor.