Multiple leader sequences for mouse cathepsin B mRNA?

We previously described the gene structure of murine cathepsin B. Our results suggested that the 5'-untranslated region (leader) is interrupted by a large intron. The second exon (exon-2) contains the translation initiation site. To characterize the leader region, a rapid amplification of cDNA ends (RACE) procedure was developed. The PCR products were directly cloned and sequenced. Nucleotide sequence analyses revealed three different 5'-cDNA ends, suggesting the existence of three different leader regions. In addition to the leader (LA) previously characterized, we now describe two other 5'-untranslated regions, LB and LC. Leader LB is located 2.3 kb upstream exon-2, and leader LC corresponds to the 3'-end of the first intron and is thus contiguous to exon-2. Our results suggest for murine cathepsin B gene the presence of multiple promoters, and possibly the expression of multiple mRNAs differing in their leader region.