Escherichia coli dnaB mutant defective in DNA initiation: isolation and properties of the dnaB protein.

Abstract

Extracts of the DNA initiation-defective mutant E. coli dnaB252 are inactive in a dnaB complementation assay but yield a ribonucleoside triphosphatase activity of native MW of about 270,000 (60,000-dalton polypeptide as subunit) that can be inactivated by antibody to dnaB. Extracts of a dnaB252 (P1bac) lysogen, in which the dnaB mutation is suppressed in vivo by the constitutive expression of the P1 dnaB analog (ban protein), are active in dnaB complementation and the activity is also sensitive to dnaB antibody. Upon further purification 2 proteins (with polypeptide MW of 60,000 and 56,000, respectively) are found associated with each other (native MW about 270,000). The larger and the smaller protein are tentatively identified as the dnaB and P1ban protein. Suppression of the dnaB mutation by prophage P1 bac may be accomplished by a stabilization of dnaB252 by P1ban subunit molecules in a heteromultimer.