Differences in the DNA-binding properties of the HMG-box domains of HMG1 and the sex-determining factor SRY.
High-mobility-group protein 1 (HMG1) is an abundant, non-sequence-specific, chromosomal protein with two homologous, HMG-box, DNA-binding domains, A and B, and an acidic tail. The HMG-box motif also occurs, as a single copy, in some sequence-specific transcription factors, e.g. the sex-determining factor, SRY. We have investigated whether or not there are differences in the DNA-binding properties of the isolated A and B HMG-box domains of HMG1 and SRY and whether, in the case of A and B, there might also be differences due to different sequence contexts within the native protein. The basic regions that flank the HMG1 B box, giving B', enhance its DNA-binding, supercoiling and DNA-bending activities, and promote the self-association of the DNA-bound B-box. All the HMG-box domains bind with structure specificity to four-way junctions, but the structure selectivity is significantly greater for A and the SRY box than for the HMG1 B or B' domains, as judged by competition with excess plasmid DNA. The domains self-associate to different extents on supercoiled DNA and this may explain differences in the ability to discriminate between four-way junctions and supercoiled DNA. The HMG1 A, B and B' domains constrain negative superhelical turns in DNA, but the SRY HMG box does not. Only the full B domain (B') bends DNA in a ligase-mediated circularisation assay; the minimal B box, the A domain and the SRY box do not. Thus, despite a common global fold, the HMG box appears to have been adapted to various functions in different protein contexts.
Teo
S H
SH
Cambridge Centre for Molecular Recognition, Department of Biochemistry, University of Cambridge, England.
Grasser
K D
KD
Thomas
J O
JO
D000595:Amino Acid Sequence; D004247:DNA / Q000378:metabolism*; D004278:DNA, Superhelical / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000378:metabolism*; D006609:High Mobility Group Proteins / Q000737:chemistry / Q000378:metabolism*; D008969:Molecular Sequence Data; D009687:Nuclear Proteins; D051876:Sex-Determining Region Y Protein; D014157:Transcription Factors / Q000378:metabolism*
D004278:DNA, Superhelical; D004268:DNA-Binding Proteins; D006609:High Mobility Group Proteins; D009687:Nuclear Proteins; D051876:Sex-Determining Region Y Protein; D014157:Transcription Factors; D004247:DNA