ULTRAVIOLET LIGHT INDUCED MUTATION AND DEOXYRIBONUCLEIC ACID REPLICATION IN BACTERIA
Through a concurrent investigation of the nonlinearity of the UV-induced mutation curve in strain WP2 and the recovery of DNA synthesis in E. coli following various ievels of exposure to UV, evidence has been obtained to support. the hypothesis that two basic radiation effects are involved in UV- induced mutation. These effects are blockage. of DNA synthesis by UV causing a requirement of RNA and protein synthesis in repair of the UV-damaged DNA synthetic system and the establishment of the photochemical modification (the mutation lesion) which results in mutation with DNA replication. The kinetic examination of recovery of DNA synthesis following UV exposure allowed the measurement of the relative increase in RNA required for recovery of DNA synthesis. The assumption is made that the amount of RNA synthesis required for recovery of DNA synthesis is directly related to the amount of damage blocking DNA synthesis and thus is a measure of the probability that the genetic region under study wili be damaged in this way. By multiplying the probability of damage of this type to the WP2 genetic region by the estimated number of mutation lesions (based on a projection to lower doses of the linear portion of the mutation frequency response curve at higher UV doses) a theoretical expression could be developed to account for the nonlinear mutation frequency response at lower UV doses. The measured mutation frequency response at lower UV doses coincided with this theoretically constructed curve, thus supporting the basic premises of the hypothesis. By means of study of the distribution of subunits of DNA obtained from growing, UV-exposed bacteria using the cesium chloride density gradient technique, it was possible to demonstrate that DNA replication is semiconservative after UV exposure, eliminatlng from consideration those hypotheses for UV-induced mutation which demand a conservative type of DNA replication. In view of the above findinigs, certain modifications in the general model for UV-induced mutation previously described by Doudney (1961) are presented and discussed. (auth)
- Research Organization:
- Univ. of Texas, Houston
- NSA Number:
- NSA-17-007836
- OSTI ID:
- 4743735
- Journal Information:
- Genetics (U.S.), Vol. Vol: 47; Other Information: Orig. Receipt Date: 31-DEC-63
- Country of Publication:
- Country unknown/Code not available
- Language:
- English
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