SFA-1, A NOVEL CELLULAR GENE INDUCED BY HUMAN T-CELL LEUKEMIA-VIRUS TYPE-1, IS A MEMBER OF THE TRANSMEMBRANE-4 SUPERFAMILY

A novel cellular gene termed SFA-1 was isolated by differential hybrid ization of a cDNA library, using probes obtained from an adult T-cell leukemia cell line in comparison with probes obtained from normal CD4( +) T cells and the MOLT-4 cell line. The mRNA of the SFA-1 gene is app roximately 1.6 kb in size and encodes a protein of 253 amino acids, co ntaining four putative transmembrane domains, a number of cysteine res idues, and one potential N-glycosylation site in a major hydrophilic r egion between the third and fourth transmembrane domains. Expression o f the SFA-1 gene was either absent or present at a low level in lympho id cells but was up-regulated after transformation by human T-cell leu kemia virus type 1 and transactivated by Tax. SFA-1 was broadly expres sed in many human cell types and conserved in different species. Compu ter-aided comparison showed that SFA-1 had significant sequence homolo gy and common structural features with members of the transmembrane 4 superfamily. SFA-1 antigen was detected as a 29-kDa membrane protein b y immunoblotting, using anti-SFA-1 monoclonal antibody.