ISSN:
1617-4623
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
Notes:
Summary UV irradiation of transforming DNA from Haemophilus influenzae, carrying a streptomycin resistance marker (Sr), results in decreased transforming activity. At high DNA concentration the “marker survival” is lower than it is at low concentration. The transition from high to low survival occurs at concentrations ranging from 2.5×10-3 to 2.5×10-2 μg/ml; in this range the probability that transformed cells take up DNA fragments in addition to the marked one increases rapidly. A similar effect of DNA concentration on the percentage of transformants is observed for a mixture of unirradiated and irradiated DNA, where virtually all of the transformants originate from the unirradiated component. This eliminates the possible explanation that the concentration dependence of UV survival of a marker reflects increasing competition for a cellular repair system. It is concluded that the lower marker survival obtained at high DNA concentration involves lethality due to UV lesions present in the additional irradiated DNA taken up by the cell. Thus the steeper marker survival curve is due to the increasing UV dose which the additional DNa necessarily receives when a marker survival curve is being established. Intergration of UV lesions rendering a chromosomal DNA strand inviable is suggested by a slight delay in cell multiplication after uptake of irradiated and — to a lesser extent — unirradiated DNA. Acriflavine at a concentration of 0.5μg/ml enhances the effect of DNA concentration on marker survival. Similarly the number of transformants obtained with unirradiated DNA in the presence of acriflavine is more strongly decreased at high than at low DNA concentration. It is suggested that each event of DNA integration involves a small change for lethality, which is enhanced if the DNA carries UV lesions or if acriflavine is present.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00433225
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