Zdeněk Neubauer

Two repressors in bacteriophage lambda

SummaryThe functions of anti-immunity and immunity are very similar: both repress the early functions acting on the same two operators, oL and oR. They differ only in their effect on the expression of the cI gene.

TOWARDS A DARWINIAN BIOSEMIOTICS. LIFE AS MUTUAL UNDERSTANDING

Contemporary understanding of the evolution of life prefers the existence of mutually isolated lineages which are indifferent to each other, and are interconnected only through their common descent. We argue that a necessary precondition for biosemiotics is communication between all coevals sharing the biosphere. It will embrace mutual custody of existing communication pathways and codes, and of common evolutionary heritage

Phase variation concerning the regulation of phage expression in non-defective λ lysogens: The involvement of prophage-derived plasmids and of the shifts in their oligomerisation

SummaryA clone containing a λ-derived cytoplasmic replicon (a λ dv-like plasmid) was obtained through thermal selection of a heat-inducible λ int6 cI857 lysogen. It still contains the original integrated prophage. Such a system can exist in two distinct regulatory phases, E1 and E2, differing both in the λ gene expression and the λ genome arrangement. In the E1 phase the expression of gene N is blocked and the plasmid is a heptamer of the fundamental unit 1.26×106 daltons, whereas in E2 phase the N gene is active and the main plasmid component is a tetramer of the same fundamental unit. Reversible transitions between E1 and E2 phases and the reestablishment of the original immune phenotype PA (parental type) accompanied by the loss of the cytoplasmic component of the λ genome take at relatively high frequencies depending on the growth and storage conditions.

Phenotype variability in a lysogen carrying a heat inducible lambda prophage

SummaryIn this preliminary report two novel regulatory states of E. coli K12 recA−(λ int6 cI857) are described in which the lytic reproduction is suppressed in the absence of immunity. Occasionally, cells can shift from one state to another.

Variations and heredity in bacterial colonies

ABSTRACT Spontaneous variation in appearance was studied in bacterial colonies of Serratia marcescens F morphotype1: (i) A defined array of non-heritable phenotype variations does appear repeatedly; (ii) The presence of colonies of different bacterial species will narrow the variability toward the typical F appearance, as if such an added environmental factor curtailed the capacity of colony morphospace; (iii) Similarly the morphospace becomes reduced by random mutations leading to new, heritable morphotypes—at the same time opening a new array of variations typical for the mutant but not accessible directly from the original F morphospace. Results are discussed in context with biphasic model of early morphogenesis applicable to all multicellular bodies.

Phage and prophage decision in defective λ-lysogens: The role of cII product

SummaryThe cII product of λ prophage plays an ambivalent role: immediately after irradiation it promotes lytic response to superinfection by the homoimmune phage, later, in some cells, it helps to reestablish immunity.

The role of cIII product and anti-immunity in zygotic induction of bacteriophage lambda

SummaryA nonlysogenic cell has twenty fold higher (26% versus 1.3%) probability to survive phage infection than entry of the same λ genome via conjugation (prophage infection). When the entering genome bears a cIII- mutation, this difference increases to one hundred fold (6% versus 0.06%). A lysogenic im- cell harbouring a defective prophage able to synthetize anti-immunity (product of gene tof) has ten fold higher probability to survive prophage infection than phage infection (20% versus 2%). Here, cIII- mutation does not affect the survival. When the cell is simultaneously infected with the phage and prophage, the decision of the phage whether to enter the lytic cycle (in im- cells) or not (in nonlysogens) is always epistatic to that of the prophage.