The results presented above indicated that the homomolecular system can provide new interesting data concerning the mechanism of RNA recombination, especially if it could be used for testing the recombination activity of RNA sequences derived from other RNA-based viruses. Consequently, we attempted to construct a universal BMV RNA3-based recombination vector called Mat0-RNA3 (for details see Materials and Methods and Figure 5A ). In Mat0-RNA3, as in the former PN0-RNA3 vector, only 3 0 -UTR was modified. It is composed of the 295 nt very 3 0 end of RNA1 followed by the 3 0 RAS cloning site, a 338 nt spacer and the 5 0 RAS cloning site.