Complexity of transcriptional regulation within the Rag locus: identification of a second Nwc promoter region within the Rag2 intron.

Nwc represents a mysterious third evolutionarily conserved gene within the Rag locus. Here, we analyzed the phenotype of Nwc(tmpro1) mice, in which the Rag2 intragenic region containing the previously identified promoter responsible for initiating transcription of Nwc in all cells except lymphocytes was deleted by homologous recombination. Despite strong nonlymphocyte-specific inhibition of Nwc transcription which runs through the regulatory region of Rag genes, their expression remained suppressed, and no developmental, morphological, anatomical, functional, physiological, or cellular defects in Nwc(tmpro1) mice could be observed. However, careful analysis of the Rag2 intergenic region uncovered a second evolutionarily conserved Nwc promoter region from which a previously unknown Nwc transcript can be generated in nonlymphocytes of Nwc(tmpro1) and normal mice. The above results reveal an unexpected additional complexity of transcriptional regulation within the Rag/Nwc locus and show that strong inhibition of Nwc transcription in nonlymphoid cells is well tolerated. Complete inactivation of Nwc is necessary to get insight into its function at transcriptional and posttranscriptional levels.