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Synthesis and characterization of a 29-amino acid residue DNA-binding peptide derived from alpha/beta-type small, acid-soluble spore proteins (SASP) of bacteria.

A 29-amino acid residue peptide (SASP-peptide) derived from the sequence of the putative DNA-contacting portion at the carboxyl terminus of an alpha/beta-type small, acid-soluble spore protein (SASP) of Bacillus subtilis has been synthesized by automated solid-phase methods and tested for its ability to interact with DNA. Circular dichroism (CD) spectroscopy reveals an interaction between this SASP-peptide and DNA, both by an increase in alpha-helix content of the peptide (which alone has a mostly random conformation) and by enhancement of the 275-nm CD band of the DNA. In contrast to results with intact alpha/beta-type SASP, however, the peptide does not induce a B----A conformational transition in the DNA. The SASP-peptide also binds to poly(dG).poly(dC) and protects this polynucleotide against DNase I digestion and UV light-induced cytosine dimer formation, parallel to findings made previously with native alpha/beta-type SASP. The results confirm the hypothesis that the carboxyl-terminal region of the alpha/beta-type SASP directly contacts DNA and possesses some, but not all, of the functional characteristics of the intact molecule.