Wollman and Jacob discovered zygotic induction. This occurs when a bacterial cell carrying the silenced DNA of a bacteriophage transfers the viral DNA along with its own DNA in its chromosome to another bacterial cell lacking the virus, causing the recipient of the DNA to break open. In the donor cell, a repressor protein encoded by the prophage (viral DNA) keeps the viral genes turned off so that virus is not produced. When DNA is transferred to the recipient cell by conjugation, the viral genes in the transferred DNA are immediately turned on because the recipient cell lacks the repressor. As a result, many viruses are made in the recipient cell, and lysis eventually occurs to release the new virus.... Zygotic induction provided insight into the nature of bacterial conjugation. It also contributed to the development of the early repression model of gene regulation that explained how the lac operon and λ bacteriophage genes are negatively regulated.