The mechanism and control of host cell lysis by bacteriophage lambda

Abstract

The lysis gene region of bacteriophage lambda, containing genes S, R, and Rz, was cloned into the plasmid pBH20. In the recombinant plasmid, the lysis genes are expressed under the control of the lacOP region. The lytic behaviour of each of the S('(+OR-))R('(+OR-))Rz('(+OR-)) alleles of the lysis operon on induction with the lac inducer, IPTG, duplicated the behaviour of the thermally-induced parental lysogens. The premature lysis phenomenon, in which addition of respiratory poisons or uncouplers causes early lysis, is also reproduced in the cloned lysis gene system. Therefore, the known lysis genes, S, R, and Rz, are the only genes required for normal lysis. The functions of the S protein were investigated. Membrane vesicles prepared from induced S('+) cells were shown to have severely reduced capacity for active transport of glucose; this defect was detectable at least 20 minutes before lysis. Cell viability was also shown to decrease very soon after induction, this decrease in viability was absolutely dependent on S expression and independent of R and Rz. The non-viable fraction of cells at any time after induction was demonstrated to be equal to the fraction committed to eventual lysis. Induction of a temperature-sensitive S allele (Sts) showed that the Sts gene product is stable and capable of inducing lysis long after cessation of synthesis of pSts. A model for S action is proposed. Polyacrylamide gel electrophoresis of subcellular fractions of the induced lysis clones showed that both pSts and pSam7 (S nonsense fragment) were present in the membrane fraction. pSts was shown to be associated with membranes of intermediate density by isopycnic sucrose density gradient centrifugation. Membrane vesicles of this density have been shown to include vesicles made from the 'zones of adhesion' between the inner and outer membranes. The Sam7 polypeptide was found to be associated with the outer membrane fractions. Three classes of mutants resistant to pS action were isolated and characterized. The properties of these mutants are described and models for their mechanism of resistance are presented.