GENETIC RECOMBINATION BETWEEN HOST-RANGE AND 



PLAQUE-TYPE MUTANTS OF BACTERIOPHAGE IN 



SINGLE BACTERIAL CELLS 1 - 2 



A. D. HERSHEY and RAQUEL ROTMAN 3 



Department of Bacteriology and Immunology, Washington University Medical School, 

 St. Louis, Missouri 



Received June 28, 1948 



WE HAVE previously shown that any two of several independently 

 arising plaque-type (r) mutants of the bacterial virus T2H interact with 

 each other, in bacterial cells infected with both, to give rise to wild type and 

 double mutant genetic recombinants (Hershey and Rotman 1948). In this 

 paper we describe comparable interactions between host-range and r mutants 

 of the same virus. The experiments furnish new information because it has 

 proved possible to count the numbers of all four types of virus found in yields 

 from the mixedly infected bacteria. 



MATERIALS AND METHODS 



The types of viral mutant to which we shall refer in this paper may be 

 summarized in terms of the mutational pattern illustrated in fig. 1. In this 

 diagram, h refers to a host-range mutant, r to any one of the rapidly lysing 

 mutants (Hershey and Rotman 1948), and m ("minute") to a mutant not 

 previously described which is characterized by a very small haloless plaque. 

 The h mutant is one which forms plaques identical in appearance and number 

 on typically sensitive strains of Escherichia coli, and on an indicator strain 

 (No. 2 B/2H, 2K) resistant to h+ forms of the virus (Hershey 1946a). All the 

 steps indicated in the diagram by arrows can be observed either as spontaneous 

 mutations, or by making the appropriate crosses. Only one example of the 

 mutant m, obtained by crossing wild type with an rtn arising in a stock of the 

 mutant r!3, has been studied. The plaques of tn and rtn are different, but are 

 not easily distinguishable, as shown in the photograph (fig. 2). 



In principle, the experimental technique we have to describe is very similar 

 to that of genetic crossing, and will be referred to in this paper in genetic 

 terms. One starts with a pair of mutants, each corresponding to a mutant 

 haploid germ cell differing from wild type by a different unit change. Bacterial 

 cells are infected with both members of the pair, and during viral growth the 

 pair interact to produce viral progeny corresponding to germ cells of a new 



1 Aided by a grant from the U. S. Public Health Service. 



7 The manuscript was prepared while the senior author held a temporary appointment in the 

 Department of Biology of the California Institute or Technology. It is a pleasure for him to 

 acknowledge material and intellectual aid received from members of the staff of that department. 



3 Present address: University of Minnesota, Minneapolis, Minn. 



[Reprinted by permission from Genetics 34:44-71, January, 1949] 



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