Summary
Transformation studies of the Challis strain of the H group of streptococcus were performed to further investigate the molecular basis of the deoxyribonucleic acid helping effect. Studies in the efficiency of transformation in the presence of non-transforming DNA support the notion that bacterial cells are indiscriminate in their uptake of donor DNA and that the helping effect occurs at a time when both transforming (T) and helping (H) DNAs have jointly entered the recipients. Furthermore, the ability of H DNA to promote transformation by T DNA is not directly altered by exposure of the former DNA to either UV-irradiation or nitrous acid. Nor does 5-bromouracil incorporation affect the capacity of H DNA to assist T DNA to transform a Challis cell.
Increasing the concentration of denatured H DNA to a level that saturates the Challis bacteria in reaction mixtures produces a significant increase in the efficiency of genetic transformation. This increase in transformation frequency is greater with single DNA strands than with the corresponding amount of double strands.
The extent of the helping effect with the Challis H DNA remains constant within an average molecular weight range of 3.5–7.0x106 daltons. In the case of heterologous E. coli DNA, however, the helping function in this range is more pronounced as a result of decreasing molecular weight, even though the net incorporation of T DNA remains unaffected. When the average M. W. is reduced below 2×106 a significant decline in the helping effect occurs in both cases.
The effect of H DNA on the genetic transfer of two nonallelic antibiotic markers demonstrates that a saturating amount of non-transforming H DNA present in cells does not enhance the likelihood of co-integration of nonallelic factors. Evidence concerning the physiology of the competent cells and their ability to be helped reveals that the physiological basis of transformabilities and the helping capabilities of a culture are not identical.
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Communicated by P. Starlinger
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Chen, KC. Further studies on the deoxyribonucleic acid helping effect during transformation. Molec. Gen. Genetics 112, 323–340 (1971). https://doi.org/10.1007/BF00334434
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DOI: https://doi.org/10.1007/BF00334434