Identification of novel exons 3' to the human SNRPN gene

The gene for the small nuclear ribonucleoprotein N (SNRPN) maps to human chromosome 15 and has 10 exons. Using cDNA cloning, direct cDNA selection, and exon-connection reverse transcriptase (RT)-PCR, we have identified three novel 3' exons of SNRPN, which have no protein coding potential. Like the other SNRPN exons, the novel exons are expressed from the paternal allele only. In contrast to several cDNA clones and RT-PCR products, however, the 3.4-kb transcript detected by Northern blot hybridization with a probe for the novel exons does not contain SNRPN. It is possible that the steady-state RNA observed in fetal tissues and in adult testis, ovary, brain, and muscle is initiated at an as yet unidentified transcription start site downstream of SNRPN or is generated by endonucleolytic cleavage of a precursor transcript, as has been shown for another imprinted gene, the insulin-like growth factor II gene.