Altered accumulation of a membrane protein unique to a membrane-deoxyribonucleic acid complex in a dna initiation mutant of Bacillus subtilis

Abstract

Membrane-deoxyribonucleic acid complexes (M-bands) have been isolated from Bacillus subtilis by their affinity for crystals of Mg2+-Sarkosyl. The membrane proteins of these complexes were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Comparison of the membrane protein composition of M-band and unfractionated membrane revealed three protein components of 125,000 (mac-1), 57,000 (mac-2), and 42,000 (mac-3) daltons unique to M-band membrane. Growth of a temperature-sensitive dna initiation mutant at the restrictive temperature resulted in an accumulation in the membrane of mac-2. This accumulation did not begin, however, until cell growth had nearly ceased, some 3 to 4 h after the cessation of deoxyribonucleic acid synthesis. Upon return of the mutant to the permissive temperature, mac-2 did not begin to return to normal levels until after the first round of deoxyribonucleic acid synthesis. A protein of 30,000 daltons, common to both M-band and whole membrane, was found to disappear from the membrane when the mutant was grown at the restrictive temperature. This disappearance is the result of increased degradation or removal from the membrane followed by a decreased rate of synthesis or insertion.