Fluorescence study of the association between gene 32 protein of bacteriophage T4 and poly(1-N6-ethenoadenylic acid). Evidence for energy transfer.

We have studied the association of gene 32 protein of bacteriophage T4 with a fluorescent polynucleotide: poly(1-N6-ethenoadenylic acid). The presence of a bridge between the N(1) nitrogen atom and the C(6) amino group of adenine bases did not alter the affinity of the protein for the polynucleotide as compared to poly(rA) and heat-denatured DNA. This suggests that this region of the nucleic acid bases is not required in protein 32-polynucleotide complexes. The formation of gene 32 protein-poly(1-N6-ethenoadenylic acid) complex resulted in an enhancement of the polynucleotide fluorescence quantum yield which could be related to a partial unstacking of the polynucleotide bases. Energy transfer at the singlet level was demonstrated from tryptophan to 1-N6-ethenoadenine residues. The efficiency of energy transfer was calculated to be 22% which is consistent with the presence of at least one of the tryptophan residues of gene 32 protein in close vicinity of the bases.