ACTIVATION AND TRANSLOCATION OF A SRC-FAMILY PROTEIN-TYROSINE KINASE IN FERTILIZED XENOPUS EGGS

摘要

Protein kinases and phosphatases are playing pivotal roles in many eukaryotic signal transduction pathways (Hunter, 1995). Protein kinases are classified into two major groups; serine/threonine-specific protein kinases and tyrosine-specific protein kinases. In most of the signal transduction cascades, activation of serine/threonine-specific kinases is preceded by the activation of tyrosine-specific protein kinases. This is probably because most of the tyrosine kinases are localized on, or beneath, the plasma membrane of the cell where the extracellular signals are accepted. Some protein kinases are not only kinases but themselves serve as transmembrane receptors. For example, receptors for platelet-derived growth factor, epidermal growth factor, nerve growth factor, and insulin are included in the receptor tyrosine kinases (van der Geer et al., 1994). Other type of protein-tyrosine kinases, represented by the Src-family kinases, are non-receptor kinases which function in conjunction with the receptor tyrosine kinases or with other intrinsic receptors such as T-cell receptor (Weiss, 1993).