Mechanisms of DNA uptake by mammalian cells: fate of exogenously added DNA monitored by the use of fluorescent dyes.

Abstract
Coprecipitation of DNA with calcium phosphate is a commonly used method of gene transfer in mammalian cells. DNA forms a tight complex with Ca Pi and DNA in this complex is resistant to nucleases present in serum or added externally. Under optimal conditions, virtually all of the recipient mouse Ltk- Aprt- cells take up Ca Pi-DNA complexes, as determined by fluorescent dyes specific for DNA (4'',6-diaminilo-2-phenylindol dihydrochloride) or for calcium salts (chlorotetracycline). Only a small proportion of the cells have detectable Ca Pi-DNA complexes in the nucleus. Uptake of the Ca Pi-DNA complexes was highly dependent upon the pH at which the Ca Pi-DNA complex was formed and upon the concentration of DNA in the complex.