The amino terminal region of the p56 lck from LSTRA exerts negative modulation on the tyrosine kinase activity.

High levels of tyrosine kinase activity have been detected in the murine lymphoma LSTRA (p56). The functional domains of this kinase have been studied by the use of antibodies generated against peptides from the amino terminal region and from the tyrosine autophosphorylation site. The amino terminal antibody had higher affinity for the p56 than the antibody directed against the phosphotyrosine site. However, the phosphorylation of exogenous substrate by p56 was lower when the tyrosine kinase was immunocomplexed by the antibody against the amino terminal region than when the kinase was complexed by the phosphorylation site antibody. This suggests that in the N-terminal region exist structures which modulate the tyrosine kinase activity of the p56.