Calcium requiring step in the uptake of deoxyribonucleic acid molecules through the surface of competent pneumococci

Abstract

The conversion of surface adsorbed deoxyribonucleic acid (DNA) molecules to a state in which they are inaccessible to exogenous deoxyribonuclease requires specifically calcium ions; magnesium ions cannot replace calcium ions. Virtually maximal levels of nuclease resistant DNA binding and genetic transformation can be obtained in media free from magnesium and containing only calcium ions. It is suggested that the calcium requiring process is the transport of DNA molecules across the plasma membrane. Magnesium ions stimulate both the loss of surface adsorbed DNA to the medium and the extracellular degradation of DNA.