Mutagen Screening with Virulent Bacteriophages

Abstract

Virus systems, and particularly those employing the T-even bacteriophages, the single-stranded DNA bacteriophages, and the temperate bacteriophage λ, have occupied the center of the molecular biologist’s arena for up to three decades. The reasons for the popularity of virus systems are as relevant now as they were in the 1930s. Viruses often excel in those properties which make microorganisms in general highly useful for genetic studies. They are easy to grow. They exhibit extremely short generation times. (The bacteriophage T4 growth cycle, encompassing about 30 min at 37°C and resulting in the release of several hundred progeny particles, corresponds to an average doubling time of about 3 to 4 min.) Genome storage is extremely simple. Virus stocks are stable for many years in the refrigerator and do not accumulate many spontaneous mutations (Drake, 1966). Extremely large populations (for instance, 10¹¹ to 10¹⁴ particles) are easily obtained, and a variety of techniques have been developed for selecting rare particles representative of events such as mutation. The relative chemical simplicity of bacteriophages, together with certain chemically unique aspects of their reproduction, has made possible a more detailed dissection of their molecular genetics than has been achieved even in the equally well-studied bacterium Escherichia coli. The formal genetics of several virus systems has been developed to a highly detailed and sophisticated level, making possible numerous genetic manipulations which render the analysis of processes such as mutation highly profitable. Finally, the pursuit of bacteriophage genetics, including even many aspects of their molecular genetics, is relatively inexpensive, particularly in comparison with metazoan systems.

The usual DNA bases are abbreviated A, T, G, and C, while the corresponding base pairs are represented by A:T and G:C. The 5-hydroxymethylcytosine of bacteriophage T4 is also abbreviated as C. Research of the author which is described here was supported by American Cancer Society Grant E59, Public Health Service Grant 04886 from the National Institute of Allergies and Infectious Diseases, and National Science Foundation Grant GB 6998.