How RNA viruses exchange their genetic material

One of the most un usual fea tures of RNA vi ruses is their enor mous ge netic vari abil­ity. Among the dif fer ent pro cesses con trib ut ing to the con tin u ous gen er a tion of new vi ral vari ants RNA re com bi na tion is of spe cial im por tance. This pro cess has been ob­served for human, animal, plant and bacterial viruses. The collected data reveal a great sus cep ti bil ity of RNA vi ruses to re com bi na tion. They also in di cate that ge netic RNA re com bi na tion (es pe cially the nonhomologous one) is a major fac tor re spon si ble for the emer gence of new vi ral strains or spe cies. Al though the for ma tion and ac cu mu la tion of vi ral recombinants was ob served in nu­mer ous RNA vi ruses, the mo lec u lar ba sis of this phe nom e non was stud ied in only a few vi ral spe cies. Among them, brome mo saic vi rus (BMV), a model (+)RNA vi rus of­fers the best op por tu ni ties to in ves ti gate var i ous as pects of ge netic RNA re com bi na­tion in vivo. Unlike any other, the BMV-based system enables homologous and nonhomologous re com bi na tion stud ies at both the pro tein and RNA lev els. As a con se­quence, BMV is the vi rus for which the struc tural re quire ments for ge netic RNA re- com bi na tion have been most pre cisely es tab lished. Nev er the less, the pre vi ously pro­posed model of ge netic re com bi na tion in BMV still had one weak ness: it could not re­ally ex plain the role of RNA struc ture in nonhomologous re com bi na tion. Re cent discoveries concerning the latter problem give us a chance to fill this gap. That is why in this re view we pres ent and thor oughly dis cuss all re sults con cern ing nonhomologous recombination in BMV that have been ob tained un til now.