Thy-1 cDNA sequence suggests a novel regulatory mechanism

Abstract
Thy-1 was originally defined in mice as a cell-surface alloantigen of thymus and brain with two allelic forms, Thy-1.1 and Thy-1.2 (ref. 1). Subsequently, the Thy-1.1 alloantigenic determinant was identified in rats2. In both species, Thy-1 is present in large amounts on thymus and brain cells3 and in smaller quantities on fibroblasts4, epidermal cells5, mammary glands6 and immature skeletal muscle7. In many of these tissues the level of Thy-1 expression changes dramatically during cell differentiation. The molecules expressing the Thy-1 antigenic determinant have been isolated from rat and mouse brain cells and have been shown to have a molecular weight of 17,500 (ref. 8). One-third of the Thy-1 molecule is carbohydrate and the remainder is a polypeptide of 111 amino acids whose sequence has been fully determined9. We report here the isolation and characterization of a cDNA clone encoding the rat thymus Thy-1 antigen but find that the DNA sequence ends prematurely at a position corresponding to amino acid 103. It appears to be a complete transcript, however, as the last codon is followed directly by a poly(A) tract.