Structural organization of the gene encoding rat cystatin β

Abstract

A genomic DNA clone encompassing the gene ( cyβ) encoding rat cystatin β (Cyβ) was isolated by screening with a rat cyβ cDNA as a probe. The gene spans about 2.6 kb and comprises three exons. The first intron is located between Lys 22 and Val 23 and the second between Lys 56 and Val 57 in the deduced amino acid sequence of Cyβ. The second exon contains the highly conserved QVVAG sequence which, unlike the sequence of other cystatin family members, is not split by an intron. In the 5′-upstream region, three SP-1-binding sites exist, but no typical TATA-box or CAAT-box sequences are found. The difference in the organization of the rat cyβ gene, encoding a family-1 cystatin, from that encoding members of the other cystatin families, suggests that cyβ diverged from a common ancestral gene earlier than the separation of genes encoding family-2 and family-3 cystatins.