During the course of a screening procedure designed to isolate gene products that mediate avian lymphocyte apoptosis, a 1070 bp cDNA encoding a 242 amino acid protein, cThy28 (GenBank accession number U34350), was isolated. Based on the deduced amino acid sequence, cThy28 is a conserved protein that shares greater than 90% amino acid similarity with several putative mammalian homologues. A structural analysis of the protein suggests that is a nuclear-localized, phosphoprotein with potential glycosylation and myristolation sites. Compared to other non-lymphoid tissues, the cThy28 protein and its transcript are present in immune organs at elevated levels. When the expression of cThy28 was analyzed in cultured bursal lymphocytes undergoing apoptosis, the cellular levels of this protein and its transcript declined and underwent degradative processes as a function of the apoptotic process. Treatment of lymphocytes with phorbol esters inhibited apoptosis and protected the cellular levels of the cThy28 protein and its transcript from undergoing this degradative process; however, analysis of transcripts of a "housekeeping" gene, GAPDH (glyceraldehyde phosphate dehydrogenase), revealed a similar response to this apoptosis treatment regimen. Thus, the apoptotic-mediated alterations in cThy28 expression and its role in lymphocyte function remain undefined; however, the potential task of this gene in apoptosis may be related to the putative functions of the cThy28 mammalian homologues identified in this report.