Sequence encoding an 'isoTarget' cassette has been inserted into the endogenous Rdl locus, in the last exon, immediately upstream of the 3'UTR. The isoTarget cassette consists of 1. an RSRT cassette containing a translational stop site and 2. a Tag:V5 epitope. This results in a conditionally tagged allele; RSR recombinase can be used to excise the RSRT cassette to produce a Tag:V5-tagged protein.