Date of Award

Summer 1957

Degree Type

Thesis - Restricted

Degree Name

Master of Science (MS)




During recent years much evidence has accumulated to suggest that deoxyribonucleic acid (DNA) is a carrier of the genetic specificity of cells. Studies of transforming principles obtained from pneumococcal and Hemophilus cells have provided a considerable part of this evidence. In 1944 Avery, MacLeod and McCarty showed that a DNA fraction isolated from Type III pneumococci was capable of transforming unencapsulated R variants derived from pneumococcus Type II into fully encapsulated Type III cells. These investigators suggested (1944) that the techniques used in such transformation studies offer a sensitive means of determining specific differences in the biological behavior of deoxyribonucleic acids. Subsequent work of the Rockefeller group and other investigators (for example, Zamenhof, Alexander and Leidy, 1953) has amply confirmed this view. The highly polymerized deoxyribonucleic acids that have been found to have transforming activity have all been extracted from intracellular locations. Recently, Catlin (1956) has reported the presence of a highly polymerized extracellular DNA in cultures of several species of bacteria. In view of the known tendency of bacterial populations to undergo rapid changes in genetic composition, a question of considerable interest concerns the possible genetic capacity of extracellular DNA. A study of this question has been undertaken, using transformation techniques comparable to those developed by Alexander and Leidy (1953) for inducing streptomycin resistance in a population of Hemophilus influenzae cells, which was initially sensitive to streptomycin. The genetic capacity of five preparations of DNA from bacteria has been investigated: intracellular DNA from H. influenzae: intracellular and extracellular DNA preparations from Micrococcus Lysodeikticus and from Pseudomonas fluorescens.



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