Differential Response to Cytochalasin B Among Cells Transformed by DNA and RNA Tumor Viruses 1, 2

adenovirus type 7, Kirsten mouse sarcoma virus (Ki·MuSV), Moloney mouse sarcoma virus, and Rous sarcoma virus. All cultures of transformed cells grew to high concentration densi· ties. Normal and transformed cells were treated with cytochal· asin B (CB) at concentrations preventing cytoplasmic cleav· age. Cells altered by DNA tumor viruses responded to CB with numerous nuclear divisions resulting in highly multinucleated cells. All but one line of cells transformed by RNA tumor vi· ruses responded to CB with usually only one and occasionally two nuclear divisions. Only birrucleated cells were formed. One clone of CB·treated BALB/c mouse embryo fibroblasts trans· formed by Ki·MuSV showed numerous cells with four and five nuclei. However, in contrast to cells transformed by DNA vi· ruses, few cells had seven or more nuclei. These results sug· gest that, in the presence of CB, cells transformed by DN