Defective transforming capacity of adenovirus type 5 host-range mutants

Host-range (hr) mutants of human adenovirus type 5 (Ad 5), selected for their ability to grow preferentially on transformed human embryo kidney cells (293 cells) and shown to fall into two complementation groups (I and II), have been tested for ability to transform rat embryo, rat embryo brain, and baby rat kidney cells. When embryo or embryo brain cells were used, mutants of both complementation groups either failed to transform or transformed at a frequency much lower than that observed with wild-type (wt) virus. Moreover, the small number of transformed colonies which did arise in hr-infected cultures failed to grow when isolated and subcultured, unlike wt transformants from which lines could be established with a high success rate. When assays were carried out with baby rat kidney cells,hr mutants of complementation group II were again transformation negative, while mutants of group I induced transformation with several times the efficiency of wt Ad 5. Again, attempts to establish transformed lines from single hr-transformed foci were consistently unsuccessful, in contrast to an almost 100% success rate with wild-type transformants; hr mutant-transformed lines could only be established with difficulty by passaging whole cultures. Our results are consistent with the idea that group I mutants are able to initiate an abortive or abnormal transformation but are defective in some aspects of its maintenance; group II mutants, on the other hand, appear to be defective in initiation of transformation.