Construction of phi29 DNA-packaging RNA monomers, dimers, and trimers with variable sizes and shapes as potential parts for nanodevices.

Recently, DNA and RNA have been under extensive scrutiny with regard to their feasibility as parts in nanotechnology. The DNA-packaging motor of bacterial virus phi29 contains six copies of pRNA molecules, which together form a hexameric ring as a crucial part of the motor. This ring is formed via hand-in-hand interaction by Watson-Crick base pairing of four nucleotides from the left and right loops. Here we report that this pRNA tends to form a circular ring by hand-in-hand contact even when in dimer or trimer form, thus implying that the pRNA structure is flexible. Stable dimers and trimers have been formed from the monomer unit in a protein-free environment with nearly 100% efficiency. The dimers and trimers could be isolated by density gradient sedimentation or purified from native gel. Dimers and trimers were resistant to pH levels as low as 4 and as high as 10, to temperatures as low as -70 degrees C and as high as 80 degrees C, and to high salt concentrations such as 2 M NaCl and 2 M MgCl2. Further study showed that pRNA dimers or trimers with variable lengths could be constructed. Seventy-five bases were found to be the central component in this formation. The elongation of RNA at the 3' end up to 120 bases did not hinder their formation. Other conditions, including the salt requirement for the formation of monomers, dimers, and trimers, have been investigated. RNA monomers, dimers, and trimers with variable lengths are potential parts for nanodevices.