Physical heterogeneity among Bacillus subtilis deoxyribonucleic acid molecules carrying particular genetic markers.

In a Bacillus subtilis deoxyribonucleic acid (DNA) preparation, extracted and purified by the Marmur procedure, the DNA molecules carrying a particular marker are heterogeneous with respect to molecular weight, buoyant density, and thermal stability. This finding constitutes evidence against unique points of breakage during DNA isolation. The variation in buoyant density suggests a local compositional heterogeneity in the chromosomal region of certain markers. The variation in molecular weight provides an explanation for the results of certain transformation experiments that are otherwise poorly understood. An example of such a result is the observation that acridine orange increases the efficiency of differential thermal inactivation of markers. An explanation of this phenomenon is suggested by the demonstration that acridine orange can decrease the natural intramarker heterogeneity in melting behavior.