Question

explain lysogeny with reference to lamba phaseex

Answer 1

Lysis versus Lysogeny 1.1 Lysis The lysis-lysogeny decision of the temperate lambda phage has emerged as a novel paradigm for understanding developmental genetic networks. E.coli and the lambda phage establish synergistic relationships. The lambda phage may exist in a dormant lysogenic state, passively replicating with the host chromosome or may fall into the lytic cycle generating progeny phages, killing their hosts. The lambda phage therefore makes a decision to follow either the lytic or the lysogenic pathway. When the lambda phage follows the lytic pathway, it replicates its DNA autonomously, expresses a set of genes, and assembles the virions, resulting in lysis of the host. If the lysogenic state continues over a long time, a stable lysogen is established in the circuit and the prophage is integrated to the host genome. This turns OFF the expression of the lytic genes. Inducing signals like UV light that damage the DNA, force the lambda phage to a SOS response and the lysogenic state switches irreversibly to the lytic phase as shown in Fig 1. The lambda phage thus behaves as a biphasic switch. Fig 1. Growth and induction of the Lambda lysogen