SKAP‐HOM, a novel adaptor protein homologous to the FYN‐associated protein SKAP551

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Abstract
A recombinant GST‐Fyn‐SH2 domain was used to purify proteins from lysates of pervanadate treated EL4 cells. N‐terminal sequencing and molecular cloning of one of the purified polypeptides resulted in the identification of a novel adaptor protein that shares strong structural homology to the recently cloned Fyn‐associated adaptor protein SKAP55. This protein was termed SKAP‐HOM (55 ologue). Despite their striking homology, SKAP55 and SKAP‐HOM have distinct characteristics. Thus, unlike SKAP55, which is exclusively expressed in T lymphocytes, SKAP‐HOM expression is ubiquitous. Furthermore, while SKAP55 is constitutively tyrosine phosphorylated in resting human T cells, SKAP‐HOM is expressed as a non‐phosphorylated protein in the absence of external stimulus but becomes phosphorylated following T cell activation. In addition, SKAP‐HOM does not associate with p59fyn in T cells although it represents a specific substrate for the kinase in COS cells. Finally, we demonstrate that, as previously shown for SKAP55, SKAP‐HOM interacts with the recently identified polypeptide SLAP‐130.

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