Cooper J A, Runge K
Department of Cell Biology, Fred Hutchinson Cancer Research Center, Seattle, Washington 98104.
Oncogene Res. 1987 Sep-Oct;1(4):297-310.
Avian pp60c-src, a proto-oncogene product, has been expressed in the yeast, Saccharomyces cerevisiae. pp60c-src from yeast is 10- to 15-fold more active than pp60c-src from mammalian fibroblasts. Extensive phosphorylation of pp60c-src occurs at tyrosine 527 in fibroblasts and inhibits pp60c-src kinase activity. In contrast, pp60c-src from yeast has low levels of phosphate at tyrosine 527. This phosphate may be added by an autophosphorylation reaction that is detectable when immunoprecipitates containing pp60c-src from yeast are incubated with ATP in vitro. This reaction is minor when compared with autophosphorylation at the principal site, tyrosine 416. These data suggest that pp60c-src in fibroblasts is normally inhibited by trans-acting factors, that either directly catalyze phosphate transfer to tyrosine 527 or augment autophosphorylation at this site. Such factors would have the potential to regulate pp60c-src kinase activity. The low but detectable ability of pp60c-src to autophosphorylate at an inhibitory site raises the possibility that pp60c-src may also be auto-regulated.
禽类原癌基因产物pp60c-src已在酿酒酵母中表达。酵母中的pp60c-src比哺乳动物成纤维细胞中的pp60c-src活性高10至15倍。成纤维细胞中的pp60c-src在酪氨酸527处发生广泛磷酸化，从而抑制pp60c-src激酶活性。相比之下，酵母中的pp60c-src在酪氨酸527处的磷酸化水平较低。这种磷酸化可能是由自磷酸化反应添加的，当含有酵母pp60c-src的免疫沉淀物在体外与ATP孵育时，这种反应是可检测到的。与主要位点酪氨酸416处的自磷酸化相比，该反应较小。这些数据表明，成纤维细胞中的pp60c-src通常受到反式作用因子的抑制，这些因子要么直接催化磷酸转移到酪氨酸527，要么增强该位点的自磷酸化。这些因子有可能调节pp60c-src激酶活性。pp60c-src在抑制位点进行自磷酸化的能力较低但可检测到，这增加了pp60c-src也可能进行自我调节的可能性。
