Genetic and biochemical analysis of transformation by pp60(src)

Very little is known about the cellular proteins that either regulate the transforming activity or mediate the phenotypic effects of pp60$\sp{src}$. The goal of the work described in this dissertation was to identify these cellular proteins, first with genetic and subsequently with biochemical analysis.

In order to identify mutations that augment the transforming activity of c-src, cells containing 8 times the normal level of pp60$\sp{c-src}$ were mutagenized and transformed revertants were isolated. Sixteen genetic revertants were characterized, each one harboring transforming mutations in cellular genes that act independently of c-src.

Despite functional similarities to the receptor class of tyrosine kinases, pp60$\sp{src}$ lacks functionally important domains found in the receptors: a transmembrane sequence, for mediating the association with membranes; a hydrophobic signal sequence for targeting the protein to the appropriate membranes; and a ligand-binding domain for regulating the kinase activity. In order to identify domains that perform these functions, mutant forms of pp60$\sp{src}$ and proteins encoded by hybrid src-pyruvate kinase genes were analysed for association with membranes and subcellular localization. These experiments demonstrate: that amino acids 1-7 of pp60$\sp{src}$ act as a recognition sequence for N-terminal myristylation, and that lysine-7 is a critical component of this sequence; that N-terminal myristylation is not sufficient to cause membrane-association; that pp60$\sp{src}$ contains multiple domains which together with N-terminal myristylation cause membrane-association; and that these membrane-anchoring domains target proteins to specific subcellular locations.

To determine whether membrane-anchoring domains act as binding sites for other cellular proteins, methods were developed for analyzing proteins that bind to pp60$\sp{src}$. These methods were used to identify a 97 kilodalton protein found in platelets which appears to bind to pp60$\sp{src}$ specifically.