Nuclear magnetic resonance structure of the prohead RNA E-loop hairpin.

The Bacillus subtilis phage phi29 packaging motor requires prohead RNA for genome encapsidation. The nuclear magnetic resonance structure of the prohead RNA E-loop hairpin, r(5'AUUGAGUU), is presented and compared to predictions from MC-SYM. The prohead RNA E-loop hairpins contain sequences similar to rRNA hairpins. Comparison of predicted and experimentally determined prohead and ribosomal hairpin structures reveals that sequence similarity is a stronger determinant of hairpin structural similarity than grouping similar types of RNA. All the hairpins contain a U-turn motif but differ in the first noncanonical pair and backbone orientation. These structures provide benchmarks for further improvements in RNA structure predictions from sequence.