Use of long RT-PCR to characterize splice variant mRNAs.

Recent advances in long reverse transcription (RT)-PCR technology allow the copying of full-length coding regions of large mRNAs in one step. Using long RT-PCR, one can be certain that a given cDNA is derived from a single mRNA. In what to our knowledge is a novel application, we can isolate and characterize splice variants for any given mRNA in a systematic manner. We optimized long RT-PCR to copy the full-length coding region of human multidrug resistance (MDR1) mRNA or the major vault protein (MVP) mRNA in one step, so that only one full-length PCR product was synthesized in each case. Such stringent conditions are necessary to ensure that smaller than full-length products derived from total cell RNA are true splice variants. Twenty MDR1 double-stranded (ds) cDNAs, isolated from either the full-length or one prominent splice-variant DNA band, visualized on agarose gels, were cloned and sequenced. Two were full-length, wild-type in sequence as expected, and the rest were splice-variant mRNAs. Fourteen of the clones were identical and encoded a prominent splice-variant mRNA that can be detected in two tumor cell lines. This approach is shown to be generally applicable to the systematic analysis of splice-variant mRNAs derived from any gene.