The molecules and methods of the present invention provide a means for in
vivo production of a trans-spliced molecule in a selected subset of
cells. The pre-trans-splicing molecules of the invention are substrates
for a trans-splicing reaction between the pre-trans-splicing molecules
and a pre-mRNA which is uniquely expressed in the specific target cells.
The in vivo trans-splicing reaction provides a novel mRNA which is
functional as mRNA or encodes a protein to be expressed in the target
cells. The expression product of the mRNA is a protein of therapeutic
value to the cell or host organism a toxin which causes killing of the
specific cells or a novel protein not normally present in such cells. The
invention further provides PTMs that have been genetically engineered for
the identification of exon/intron boundaries of pre-mRNA molecules using
an exon tagging method. The PTMs of the invention can also be designed to
result in the production of chimeric RNA encoding for peptide affinity
purification tags which can be used to purify and identify proteins
expressed in a specific cell type.