To this end two RNA3 molecules, prototypes of a new vector carrying two RASes, were prepared. To obtain them we used PN0-RNA3, described earlier, and a well-characterized recombinationally active sequence from BMV RNA1 (RAS1, see Figure 1 ). The 137 nt RAS1 corresponding to RNA1 between positions 2856 and 2992 was inserted into the PN0-RNA3 RAS cloning site, in antisense (RAS1as) and sense (RAS1s) orientations ( Figure 2 ). As a result, we obtained Mag1-and MagH-RNA3 derivatives (30) . Then the 356 nt portion of Mag1-and MagH-RNA3 3 0 end was replaced with a 379 nt sequence representing the wtRNA1 3 0 end (fragment encompassing the entire 3 0 -UTR and RAS1s sequence) ( Figure 2 ). In addition, a marker mutation (called DXho) was introduced within the RNA1-derived fragment to make it distinguishable from an analogous region present in wtRNA1. To this end, the XhoI restriction site (2988-2994) was disrupted by a 4 nt insertion (GATC) between C-2991 and G-2992. Resultant RNA3 derivatives, called MatNH-and MatH-RNA3, have unchanged 5 0 -UTR, intergenic and coding regions and a highly modified 3 0 -UTR. The latter includes 3 0 -UTR coming from wtRNA1 and two RAS1 sequences (3 0 RAS1 and 5 0 RAS1) separated by a 338 nt spacer (sequence CCMV and B1). In MatNH-RNA3, 3 0 RAS1 is located in sense and 5 0 RAS1 in antisense orientation, while in MatH-RNA3 both RAS1 sequences are in sense orientation ( Figure 2 ).