DNA-binding property of the novel DNA-binding domain STPR in FMBP-1 of the silkworm Bombyx mori.

The STPR domain is a novel DNA-binding domain composed of repeats of 23 amino-acid-long peptide found in the fibroin-modulator-binding protein-1 (FMBP-1) of the silkworm Bombyx mori. Theoretical proteins having the STPR domain are highly conserved, particularly in vertebrates, but the functions are mostly unknown. In this study, the DNA-binding property of the STPR domain in FMBP-1 was examined. Use of reagents selecting the DNA groove and an oligonucleotide in which the dA:dT pairs of the probe were replaced with dI:dC pairs in mobility shift assay demonstrated that FMBP-1 approaches DNA from the major groove. Permutation electrophoresis using probes of the same length but containing the FMBP-1-binding site at different positions showed that FMBP-1 bends DNA through its binding. To induce the sharp bend of DNA, the STPR domain alone was insufficient and the long N-terminal extending region was necessary. Moreover, the basic region extending from the N-terminus of the STPR domain stabilized the DNA binding of the STPR domain. These results suggested that DNA-binding properties of the STPR domain are affected strongly by the structure of the flanking regions in the STPR domain-containing proteins.

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