Deletion in a recombinant retroviral vector resulting from a cryptic splice donor signal in the moloney leukemia virus envelope gene

Proviral DNA derived from a recombinant retroviral vector (LHM₁PL), constructed to transduce the human purine nucleoside phosphorylase coding region along with the mouse metallothionein I promoter, was molecularly cloned in order to characterize a deletion previously observed in this provirus. Nucleotide sequence comparison with the original retroviral vector construct revealed two deletions in the cloned provirus. One of the deleted regions originated entirely from within the mouse metallothionein promoter. A second deletion eliminated portions of both viral and metallothionein promoter sequences. All four deletion junctions in the original construct included sequences which conform to those proposed as eukaryotic consensus splice donor and acceptor signals, including a previously unreported cryptic splice donor signal in the Moloney leukemia virus envelope gene. It is concluded that RNA splicing between inadvertently juxtaposed donor and acceptor signals was responsible for the observed deletions.