An Experiment Is Performed in Which a Point Mutation Is $\zeta$

Multiple Choice

An experiment is performed in which a point mutation is introduced randomly into the Zap-70 gene for a particular strain of mice.The mutant mice display a defect in T cell development.However,precursor T cells isolated from the thymus of these mice show normal expression levels of Zap-70 of the correct molecular weight.On further in vitro analysis,the mutant Zap-70 is found to bind to ITAM motifs in the cytoplasmic tail of the $\zeta$ chain,but only when the $\zeta$ chain is phosphorylated.No phosphorylated LAT is detected,however.Given these data,in which of the following protein domains is the mutation most likely to be present?

A) Pleckstrin homology (PH) domain
B) Proline-rich (PR) domain
C) SH1 domain
D) SH2 domain
E) SH3 domain