EXON SKIPPING IN THE EXPRESSION OF THE GENE IMMEDIATELY UPSTREAM OF N-RAS (UNR NRU)

The unr (or NRU) gene was identified during investigations of the structure of the N-ras locus in the genome of mammals. A striking feature of the unr/N-ras gene tandem is the short intergenic distance of 150 nucleotides which suggests the possibility of transcriptional interactions between the two genes. At present, the function of the unr gene is unknown, but the predicted translation product shows a distant relationship to a class of DNA binding proteins. Comparison of the two published cDNA sequences, from a human lymphocytic and a rat testis cDNA library, reveals a difference of 31 amino acids in the size of the predicted proteins. We show here that this is due to the skipping of exon 5 within the human NRU gene and that a similar phenomenon occurs in the rat unr gene. Exon skipping takes place in all the cells and tissues we have analyzed and generates the predominant form of message, except in the brain where both classes are about as abundant. This exon skipping is independent of other aspects of unr expression such as the choice of the polyadenylation site.