Liebl E C, England L J, Martin G S
Department of Molecular and Cell Biology, University of California, Berkeley 94720.
Virology. 1993 Jul;195(1):265-7. doi: 10.1006/viro.1993.1371.
XD4 is a host range deletion mutant (delta 77-225) of the v-src transforming gene. This mutant transforms chicken embryo fibroblasts (CEF) but not Rat-2 cells. It encodes a product (XD4-src) that is phosphorylated at tyrosine and active as a tyrosine kinase in CEF, but is neither phosphorylated at tyrosine nor active as a kinase in Rat-2 cells. We report here that the XD4-src kinase activity in Rat-2 cells can be restored by co-expression with the tyrosine kinase encoded by v-fps, but not by co-expression with activated Ha-ras. Mutation of the major tyrosine autophosphorylation site (Y416) in XD4-src reduced but did not abolish the reactivation of XD4 tyrosine phosphorylation and kinase activity by v-fps. These results suggest that deletion of the SH2 and SH3 domains renders v-src kinase activity dependent on tyrosine phosphorylation at Y416 and other sites. The reactivation of XD4-src may result either from direct phosphorylation by the v-fps gene product or may be an indirect consequence of v-fps expression.
XD4是v-src转化基因的宿主范围缺失突变体（缺失77 - 225位）。该突变体能转化鸡胚成纤维细胞（CEF），但不能转化Rat-2细胞。它编码一种产物（XD4-src），该产物在CEF中酪氨酸磷酸化且作为酪氨酸激酶具有活性，但在Rat-2细胞中既不发生酪氨酸磷酸化也不具有激酶活性。我们在此报告，通过与v-fps编码的酪氨酸激酶共表达可恢复Rat-2细胞中的XD4-src激酶活性，但与活化的Ha-ras共表达则不能。XD4-src中主要酪氨酸自磷酸化位点（Y416）的突变降低了但并未消除v-fps对XD4酪氨酸磷酸化和激酶活性的再激活作用。这些结果表明，SH2和SH3结构域的缺失使v-src激酶活性依赖于Y416和其他位点的酪氨酸磷酸化。XD4-src的再激活可能是由于v-fps基因产物的直接磷酸化，也可能是v-fps表达的间接结果。
