Properties of a mutant of Escherichia coli defective in bacteriophage λ head formation ( groE) : II. The propagation of phage λ

Abstract

In the accompanying paper (Sternberg, 1973) the properties of three independently isolated strains of Escherichia coli with groE mutations (NS-1, NS-2 and NS-3) have been characterized. In this report the ability of these strains to propagate phage λ is examined in greater detail. In the temperature -sensitive groE strain NS-1, all early phage functions tested (curing, infective center formation, DNA synthesis and early messenger RNA synthesis) are expressed normally. In addition, two late phage functions (late mRNA synthesis and tail formation) are also expressed normally, and a third, phage-induced cell lysis, is expressed with only a slight delay. Based upon head-tail in vitro complementation assays, however, λ fails to make any functional heads at elevated temperatures (41 °C) in this host. Electron microscopic studies of strain NS-1 defective lysates indicate that aberrant head-like forms, including tubular forms and “monsters,” are made. Mutants of λ, designated λ EP, which are able to grow in the three groE strains, have been isolated. An analysis of these mutants indicates that at least some carry a mutation in λ head gene E and these make reduced levels of active gene E protein in groE hosts. A further study of all known λ head genes indicates that it is the interaction between the gene E protein and the proteins specified by head genes B and C that is adversely affected by the groE mutation. Presumably, the relative level of gene E protein is too high in groE strains for proper head formation. The λ EP mutation compensates for this effect by reducing the level of this protein, and so restoring a balance.