We showed previously that the TCR and CD2 fail to couple efficiently with their signal transduction machinery in J45.01, a CD45-deficient variant of the Jurkat T-cell line. Transfection into J45.01 of a cDNA encoding a chimeric membrane protein containing the cytoplasmic sequence of CD45 and extracellular and transmembrane sequences derived from the A2 allele of MHC class I rescues proximal signaling events after TCR stimulation. In this report, we describe rescue of CD2-mediated signaling and evaluate further the characteristics of TCR signaling in J45.01 after expression of the chimeric protein. Cells expressing the chimeric molecule demonstrate TCR- and CD2-mediated increases in PTK activity and PI turnover. Stimulation of the TCR and CD2 on the transfected cells also results in the expression of CD69 on the cell surface, a more distal signaling event. Although these measures of signal transduction via the TCR and CD2 are restored in the transfected cells, the magnitude of the responses are less than those seen in the wild-type Jurkat cells. These findings demonstrate that the cytoplasmic domain of CD45, expressed as a chimeric membrane protein, is sufficient for mediating signal transduction through CD2 as well as through the TCR complex. In addition, these results suggest that the extracellular and/or transmembrane domains of CD45 may contribute to the efficiency of signal transduction. © 1994.