Analysis of the transforming potential of the human homolog of mos

The human homology, c- mos hu, of the mouse cellular mos proto-oncogene (c- mos mu) transforms NIH 3T3 cells at low efficiency. Furthermore, the c- mos hu-induced foci are less distinct, and transformed cells contain a high level of human mos protein. The transforming activity of hybrid mos genes derived from human and mouse sequences reveals three domains within the coding region, as well as a negative regulatory sequence upstream from the c- mos hu ORF that reduces its transforming efficiency. The mos C-terminal region, however, which contains the src-kinase homology domain, appears to have the greatest influence on transforming efficiency. The low transforming efficiency of c- mos hu may provide a selective advantage to the host, but it also may indicate a reduced or modified function of mos in humans.