Membrane Association of the Deoxyribonucleic Acid Growing-Point Region in Mycoplasma gallisepticum

Abstract

Newly replicated deoxyribonucleic acid (DNA) in Mycoplasma gallisepticum A5969 is membrane associated. Cells pulse-labeled 1 to 3 min with 3 H-thymidine are lysed by a freeze-thaw procedure. After brief sonic treatment to shear the DNA, differential centrifugation gives a cell fraction (P2) that is enriched sevenfold for pulse-labeled DNA. P2 contains 80% of the total adenosine triphosphatase activity, 65% of the total cholesterol, and morphologically intact terminal bleb structures. Three to four minutes are needed to fully label the DNA growing-point region, whereas 7 to 8 min are required to “chase” 50% of the 3 H-labeled DNA. This pulse-chase removes 80 to 85% of the nascent DNA from the P2 fraction.