ASSOCIATION OF THE PROPHAGE P1BAN PROTEIN WITH THE DNAB PROTEIN OF ESCHERICHIA-COLI - OVERPRODUCTION OF BAN PROTEIN BY A P1BAC-CRR MUTANT

The constitutive synthesis of the dnaB analog (ban) protein by prophage P1bac permitted the construction of an otherwise non‐viable Escherichia coli strain bearing the unsuppressed (sup−) amber mutation dnaB266. Growth of this strain is cryosensitive and the ban protein furnished by prophage P1bac does not support bacteriophage λ replication [D'Ari et al., J. Mol. Biol. 94, 341–366 (1975)]. Recently a P1bac crr prophage mutant was isolated with the ability to confer cryoresistant (crr) growth to E. coli sup+dnaB266. The presence of prophage P1bac crr in E. coli sup−dnaB266 makes the strain permissive for λ growth [D. Touati‐Schwartz (1978) in DNA Synthesis‐Present and Future (Molineux, I. & Kohiyama, M., eds) pp. 683–692, Plenum Press, New York. P1ban protein is isolated by means of a dnaB‐complementation assay from P1bac crr lysogens of four E. coli mutants containing either thermo‐sensitive or thermo‐resistant dnaB protein. Monomers of the phage protein (ban) are found to be associated with monomers of the host dnaB protein in the form of heteromultimers as was reported earlier for P1bac lysogens [Lanka et al., J. Biol. Chem. 253, 4746–4753 (1978)]. The ban protein is, however, overproduced by P1bac crr when compared to the corresponding P1bac prophage. Overproduction of ban protein results in a thermoresistance of DNA synthesis in crude cell extracts and thermo‐resistant heteromultimers composed of ban and thermo‐sensitive dnaB subunits. The overproduction of ban protein is also demonstrated in the P1bac crr lysogen of E. coli sup+dnaB266 by precipitation with dnaB antibody. The results suggest that cryosensitive growth of E. coli sup+dnaB266 (P1bac) and its inability to support λ replication is due to a cellular deficiency in ban protein molecules rather than to an inefficacy of ban in the absence of an effective dnaB protein. Copyright © 1979, Wiley Blackwell. All rights reserved