EXON-2 OF HUMAN CATHEPSIN-B DERIVES FROM AN ALU ELEMENT

Transcripts for the cysteine protease cathepsin B are alternatively sp liced in the untranslated regions (UTRs). We show that a cathepsin B p robe containing 5'-UTR sequences hybridized to an RNA of similar to 30 0 nt in addition to the typical 2.2 and 4.0 kbp mRNAs, Within this 5'- UTR, exon 2 was found to be homologous to Alu repetitive elements. Spe cifically, exon 2 was part of an Alu element interspersed with the cat hepsin B gene, The similar to 300 nt band that hybridized to our cathe psin B probe likely corresponds to Alu transcripts, which are known to accumulate in human cells. Indeed, a similarly migrating band was det ected with an authentic Alu probe. Thus, we suggest that primary trans cripts for cathepsin B contain Alu sequences which are preserved as ex :on 2 in some fully spliced mRNAs. (C) 1997 Federation of European Bio chemical Societies.