Alanine scanning and Fe-BABE probing of the bacteriophage ø29 prohead RNA-connector interaction

The DNA packaging motor of the Bacillus subtilis bacteriophage ø29 prohead is comprised in part of an oligomeric ring of 174 base RNA molecules (pRNA) positioned near the N termini of subunits of the dodecameric head-tail connector. Deletion and alanine substitution mutants in the connector protein (gp10) N terminus were assembled into proheads in Escherichia coli and the particles tested for pRNA binding and DNA-gp3 packaging in vitro. The basic amino acid residues RKR at positions 3-5 of the gp10 N terminus were central to pRNA binding during assembly of an active DNA packaging motor. Conjugation of iron(S)-1-(p-bromoacetamidobenzyl) ethylenediaminetetraacetate (Fe-BABE) to residue S170C in the narrow end of the connector, near the N terminus, permitted hydroxyl radical probing of bound [(32)P]pRNA and identified two discrete sites proximal to this residue: the C-helix at the junction of the A, C and D helices, and the E helix and the CE loop/D loop of the intermolecular base pairing site.