Abstract: The present invention provides a system for simple generation of recombinant animal viruses. The system includes a virus homing vector and can further comprise a transfer vector. These components are used in a system that reduces the number of cloning steps and provides for easier preparation of a number of recombinant viruses.

Abstract: Compounds of the formula (I) or salts thereof, ##STR1## wherein the dotted line represents a single or double bond, R.sup.1 is alkyl or amino optionally substituted by alkyl, alkanoyl or benzyl group: R.sup.2, R.sup.3, R.sup.4 and R.sup.5 are the same or different and each is selected from hydrogen, phenyl, halo, nitro, a group S(O).sub.n R.sup.8 wherein n is the integer 0, 1 or 2 and R.sup.8 is halo or alkyl or a group NR.sup.9 R.sup.10 are both hydrogen, a group NR.sup.11 R.sup.12 wherein R.sup.11 and R.sup.12 are the same or different and each is hydrogen or alkyl, a group OR.sup.13 wherein R.sup.13 is hydrogen or C.sub.1-4 alkyl substituted by halo; a C.sub.1-4 aliphatic group optionally substituted by a group OR.sup.14 or NR.sup.14 R.sup.15 wherein R.sup.14 and R.sup.15 are the same or different and each is hydrogen or alkyl; ot two of R.sup.2 to R.sup.5 are linked together to form a benzp group, one of R.sup.2 to R.sup.3 is a group X--Y--R.sup.16 wherein X is CH.sub.2, NR.sup.17, CO, or S(O).sub.