A Thy-1- mutant defining a gene acting in trans position to regulate cell-surface Thy-1 glycoprotein expression and Thy-1 messenger RNA content.

The Thy-1 glycoprotein is a differentiation antigen which exhibits tissue-specific regulation. A mutant of a Thy-1.1+ T-cell lymphoma has been isolated which does not express Thy-1 glycoprotein on the cell surface and does not accumulate Thy-1 mRNA in the cytoplasm. Hybrids between the mutant and a Thy-1.2+ T-cell lymphoma express 20-30-fold lower levels of Thy-1 glycoprotein on their cell surface compared to wild-type T-cell lymphomas, and they have correspondingly low levels of cytoplasmic Thy-1 mRNA. A revertant of one hybrid was isolated which expressed wild-type levels of both Thy-1 alleles on its surface and contained correspondingly increased levels of Thy-1 mRNA. A Thy-1+ revertant of the Thy-1- mutant was isolated by cell sorting. A second generation Thy-1- mutant could be isolated from this revertant which also did not accumulate Thy-1 mRNA and which behaved in a way similar to the first generation mutant when hybridized to a Thy-1.2+ lymphoma. No changes in the structure or copy number of the Thy-1 structural gene could be detected in this series of mutants and revertants. These properties are consistent with a mutation in one (or more) gene(s) which acts in trans position to regulate Thy-1 glycoprotein expression.