Structure and origin of a novel class of defective interfering particle of vesicular stomatitis virus

The (enone structure and terminal sequences of a 'copyback ' defective interfering (DI) particle ST1, and a novel complexly rearranged 'snapback ' DI particle ST2 of vesicular stomatitis virus have been determined. The STL DI genome SNA possesses 54 base long inverted complementary termini, the 5 ' end of which is homologous to the standard virus genome 5 ' end. Following this region of inverted complementarity the DI RNA 5 ' end continues to be homolo-gous to standard virus BNA 5 ' sequences, whereas the 3 ' end diverges into sequences within the virus L gene internal sequences. ST2 DI genome RNA does not contain colinear covalently linked plus and minus sense SNA oopies of the standard infectious virus RNA 5 ' terminus as predicted from the prototype snapback DI structure, but instead appears to be a hairpin copy of the ST1 DI RNA genome. This is the first evidence suggesting that DI particles may be generated from RNA templates other than the standard virus RNA. Generation models and the implications of these findings for RNA virus evolution are dis-cussed