Icosahedral virus-like particles (VLPs) of RNA phage Qβ are stabilized by four disulfide bonds of cysteine residues 74 and 80 within the loop between β-strands F and G (FG loop) of the monomeric subunits, which determine the five-fold and quasi-six-fold symmetry contacts of the VLPs. In order to reduce the stability of Qβ VLPs, we mutationally converted the amino acid stretch 76-ANGSCD-81 within the FG loop into the 76-VGGVEL-81 sequence. It led to production in Escherichia coli cells of aberrant rod-like Qβ VLPs, along with normal icosahedral capsids. The length of the rod-like particles exceeded 4–30 times the diameter of icosahedral Qβ VLPs.
