GENOMIC CLONING OF HUMAN THIOREDOXIN-ENCODING GENE - MAPPING OF THE TRANSCRIPTION START POINT AND ANALYSIS OF THE PROMOTER

Thioredoxin (TR) is a small ubiquitous dithiol-reductase enzyme first identified in bacteria and plants. In recent years, this protein has b een recognized as playing an important role in the growth control of e ukaryotic cells, especially in lymphocytes. It was first cloned from a human Epstein-Barr virus-transformed lymphoblastoid B-cell line by ou r group in 1988 [Wollman et al., J. Biol. Chem. 263 (1988) 15506-15512 ] and localized on chromosome 3 p11-p12 by in situ hybridization [Lafa ge-Pochitaloff-Huvale et al., FEBS Lett. 255 (1989) 89-91]. The presen t work was performed to study the genomic organization of the human th ioredoxin (hTR)-encoding gene (hTR). The screening of a human genomic library in lambdaEMBL4 phage led to the identification of two genomic clones which encompassed the entire gene, including the promoter regio n. The coding region of hTR spans over 13 kb and is organized into fiv e exons separated by four introns which were 60% sequenced. We determi ned the transcription start point (tsp) by primer extension. This tsp located, in lymphocytes, 22-bp downstream from a TATA box (TATAA) defi nes a 5' untranslated region of 74 bp. We analyzed 2149-bp upstream fr om the promoter for sequence motifs which could bind regulatory protei ns. This promoter contains many possible regulatory elements compatibl e with both a basal constitutive expression and a regulated inducible transcription, especially by cytokines such as interleukin-6 and inter ferons. Finally, Southern hybridization of genomic DNAs from several d onors detected only one active gene encoding hTR.