SUMMARY: organisms are capable of binding in deoxyribonuclease-resistant form high molecular weight double- or single-stranded homologous or heterologous deoxyribonculeate in amounts of 0·1 − 1·0 × 10 g./organism. in a temperature-dependent mode. The maximum amounts of bound DNA ranged from 25 to 125 molecules of 5 × 10 d. Transformation of streptomycin-sensitive recipients to streptomycin resistance under conditions of maximum DNA uptake was relatively rare, being about 2-4-fold higher than spontaneous mutation. Ultraviolet (u.v.) inactivation studies showed that no caffeine-inhibitable u.v. dark-repair mechanism was present. Photoreactivation was demonstrable: the PR cross-sector was 0·39. From these results it was inferred that is unable to be genetically transformed because of the absence of one or more steps which occur between irreversible DNA uptake and genetic integration. A model system which incorporates the above findings and suggests that donor DNA functions transiently in recipients is presented.


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