SEQUENCE OF A HUMAN TRANSCRIPT EXPRESSED IN T-LYMPHOCYTES AND ENCODING A FIBRINOGEN-LIKE PROTEIN

A murine cDNA sequence (termed pT49), encoding a protein related to th e fibrinogen (Fib) beta and gamma chains, has been previously reported [Koyama et al., Proc, Natl. Acad. Sci, USA 84 (1987) 1609-1613]. We u sed a murine pT49 probe to screen a human small intestine cDNA library , and obtained a set of overlapping cDNA clones encoding a Fib-like pr otein that is 80% identical with the product of the murine pT49 gene. The deduced amino acid (aa) sequence contains a predicted signal pepti de and five consensus motifs for N-linked glycosylation. The presence of conserved Cys residues involved in the assembly of the mature Fib c omplex and of two alpha-helical regions permissive for coiled-coil for mation, suggests that this Fib-like protein may be secreted as a multi chain complex. Two mRNA species of approx. 4.5 and approx, 1.5 kb were detected by Northern blot hybridization of a human pT49-homolog cDNA probe with RNA obtained from resting peripheral blood T-lymphocytes. B y RT-PCR analysis of purified peripheral blood T-lymphocyte subsets, w e found expression of the pT49-homolog transcript in both CD3(+)/CD4() and CD3(+)/CD8(+) T-lymphocytes. The coding region of the human pT49 -homolog cDNA was fused at its 3' end with a tag-coding sequence and w as expressed in CHO cells. The corresponding gene product was immunopr ecipitated with an anti-tag antibody from the cell lysate and from the culture supernatant of metabolically labeled transfectants and was id entified as approx, 62 and approx. 64-70-kDa proteins, respectively.