Translocation of the pre-synaptic complex formed upon DNA uptake by Streptococcus sanguis and its inhibition by ethidium bromide

Abstract

Donor DNA in its initially bound, singlestranded form exists in a chromosomally-unassociated complex where it is resistant to exogenous DNase I but sensitive to micrococcal nuclease. Most of the complexes are readily recuperable from the supernatant of recipients converted into spheroplasts. Subsequent to formation of this superficially located complex, donor DNA progressively associates with the recipient chromosome into which it is eventually integrated. Treatment of recipients with ethidium bromide at various times after initial DNA binding almost immediately halts translocation of whatever donor material is not yet synapsed with the chromosome. On the other hand, donor DNA that has already synapsed experiences no difficulty in becoming genetically integrated. Some degradation occurs to DNA that fails to undergo translocation as a result of ethidium bromide treatment, the acid-soluble products appearing in the culture medium. DNA in untranslocated complexes surviving treatment is not appreciably different in single-strand length from that in untreated complexes. When these surviving complexes are isolated from a cell lysate, the contained DNA can be shown by spectrofluorometry to have bound the drug.