The integrated state of viral DNA in SV40-transformed cells.

Dulbecco and his group demonstrated that the infection of normal cells with certain types of viruses (oncoviruses) led to the incorporation of virus-derived genes into the host-cell genome, and that this event lead to the transformation (the acquisition of a tumor phenotype) of those cells. Order of authorship in the original publication: Sambrook, Westphal, Srinvasan, Dulbecco. Digital facsimile from PubMedCentral at this link.

In 1975 Dulbecco shared the Nobel Prize in Physiology or Medicine with David Baltimore and Howard Temin "for their discoveries concerning the interaction between tumour viruses and the genetic material of the cell."