Potential transforming-ability by internal deletion of the bovine c-myb gene.

Two kinds of bovine c-Myb, the 75 kDa full-length (FL) c-Myb from the thymic type of sporadic bovine lymphosarcoma (SBL) cells, and 65 kDa deleted (DEL) c-Myb, which is an internally deleted form (85 amino acids corresponding to the negative regulatory domain) from calf-type SBL were found. To investigate the relationship between internal deletion and transforming capacity, we constructed retroviral vectors carrying cDNA that encoded either FL- or DEL-Myb protein, and transfected them to mouse fetal liver cells. In spite of the high trans-activating capacity of DELMyb, DELMyb and FLMyb showed no significant difference in oncogenic capability by measurement of colony formation in soft agar or in methylcellulose medium. Thus, the internal deletion of the c-myb gene is competent for transactivation but not directly relevant to transformation of mouse hemopoietic cells.