Activation of the N-terminally truncated form of the Stk receptor tyrosine kinase Sf-Stk by Friend virus-encoded gp55 is mediated by cysteine residues in the ecotropic domain of gp55 and the extracellular domain of Sf-Stk.

Activation of the N-terminally truncated form of the Stk receptor tyrosine kinase Sf-Stk by Friend virus-encoded gp55 is mediated by cysteine residues in the ecotropic domain of gp55 and the extracellular domain of Sf-Stk.