Five novel complementary DNA (cDNA) clones which are differentially expressed between two closely related T lymphoma cell clones were isolated using subtraction-enriched differential screening. SL12.4 cells, from which the cDNAs were isolated, have characteristics of thymocytes at an intermediate stage in development and cause prominent extranodal ovarian tumors in syngeneic animals. A sister cell clone, SL12.3, derived from the same tumor, has a distinct phenotype and causes more aggressive,

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... ffuse lymphomas. Four of the five novel genes are expressed in normal thymus, activated spleen cells, or gut-associated lymphoid tissue. The DNA sequence and predicted protein sequence are presented for one of the novel cDNA clones. This novel cDNA clone detects mRNA in normal thymus, gut-associated lymphoid tissue, and ovarian tissue. The predicted protein has four putative transmembrane-spanning regions. The expression of the transcript is repressed in somatic cell hybrids formed from SL12.4 cells fused with three different T lymphoma cell lines which lack detectable mRNA complementary to the novel cDNA clone. This trans-negative regulation suggests that the expression of the gene is regulated by repressional mechanisms.