by the observation that a dose of MMC that allows survival of only 1 in 1,000 monocomplexes allows survival of about 70% of multicomplexes. Similar multicomplex survival curves (without shoulders) were also obtained for the DNA damaging agents P32 decay, psoralen plus near-UV irradiation (PUVA), N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), methyl methane sulfonate (MMS) and nitrous acid. Several of the genes found to be necessary for MR in virus T4 proved to be orthologs for genes essential for recombination in prokaryotes, eukaryotes and archaea. This includes, for instance, T4 gene uvsX which specifies a protein that has three-dimensional structural homology to RecA from Escherichia coli and the homologous protein RAD51 in eukaryotes and RadA in archaea. It has been suggested that the efficient and accurate recombinational repair of DNA damages during MR may be analogous to the recombinational repair process that occurs during meiosis in eukaryotes. History Bacteriophages were first discovered by the English scientist Frederick Twort in 1915 and Félix d'Hérelle in 1917. In the late 1930s, T. L. Rakieten proposed either a mixture of raw sewerage or a lysate from E. coli infected with raw sewerage to the two researchers Milislav Demerec and Ugo Fano. These two researchers isolated T3, T4, T5, and T6 from E.coli. Also, in 1932, the researcher J. Bronfenbrenner had studied and worked on the T2 phage, at which the T2 phage was isolated from the virus. This isolation was made from a fecal material rather than from sewerage. At any rate, Max Delbrück was involved in the discovery of the T even phages. His part was naming the bacteriophages into Type 1(T1), Type 2 (T2), Type 3 (T3), etc. The specific time and place of T4 virus isolation remains unclear, though they were likely found in sewage or fecal material. T4 and similar viruses were described in a paper by Thomas F. Anderson, Max Delbrück, and Milislav Demerec in November 1944. In 1943, Salvador Luria and Delbrück showed that bacterial mutations for phage resistance arise in the absence of selection, rather than being a response to selection. The traditional wisdom among bacteriologists prior to 1943 was that bacteria had no chromosomes and no genes. The Luria–Delbrück experiment showed that bacteria, like other established model genetic organisms, have genes, and that these can spontaneously mutate to generate mutants that may then reproduce to form clonal lineages. That year, they also began working with Alfred Hershey, another phage