MUTATIONAL ANALYSIS OF THE DNA-BINDING DOMAIN-A OF CHROMOSOMAL PROTEIN HMG1

We have mutated several residues of the first of the two HMG-boxes of mammalian HMG1. Some mutants cannot be produced in Escherichia coli, s uggesting that the peptide fold is grossly disrupted. A few others can be produced efficiently and have normal DNA binding affinity and spec ificity; however, they are more sensitive towards heating and chaotrop ic agents than the wild type polypeptide. Significantly, the mutation of the single most conserved residue in the rather diverged HMG-box fa mily falls in this 'in vitro temperature-sensitive' category, rather t han in the non-folded category. Finally, two other mutants have reduce d DNA binding affinity but unchanged binding specificity. Overall, it appears that whenever the HMG-box can fold, it will interact specifica lly with kinked DNA.