What is Xis gene?

In molecular biology, excisionase is a bacteriophage protein encoded by the Xis gene. It is involved in excisive recombination by regulating the assembly of the excisive intasome and by inhibiting viral integration.

What is the function of excisionase?

During excision, excisionase (Xis) helps Int to bind DNA and introduces a bend in the DNA that facilitates formation of the proper excisive nucleoprotein complex. The carboxyl-terminal α-helix of Xis is thought to interact with Int through direct protein-protein interactions.

What is lambda gene?

Enterobacteria phage λ (lambda phage, coliphage λ, officially Escherichia virus Lambda) is a bacterial virus, or bacteriophage, that infects the bacterial species Escherichia coli (E. coli). It was discovered by Esther Lederberg in 1950.

What is the source of the Lambda λ DNA?

Lambda DNA, a linear, double-stranded phage DNA containing 12 bp single-stranded complementary 5′-ends, is derived from an Escherichia coli bacteriophage (Bacteriophage lambda cI857 Sam7).

How many genes does lambda have?

Bacteriophage lambda is a model phage for most other dsDNA phages and has been studied for over 60 years. Although it is probably the best-characterized phage there are still about 20 poorly understood open reading frames in its 48-kb genome.

What has lambda done for us?

Studies with λ have contributed much to our understanding of the molecular basis of these processes, their biological and evolutionary roles, and how they have been harnessed by experimenters, most particularly in the development of recombinant DNA technologies.

What are cos sites?

The cos site represents the junction between two genomes in a concatemer and serves as the packaging initiation site. Unlike the pac sequences of viruses that use the head-full packaging mechanism, cos also serves as a specific packaging termination sequence.

When does lambda phage integrate into the host chromosome?

Lambda phage. However, under certain conditions, the phage DNA may integrate itself into the host cell chromosome in the lysogenic pathway. In this state, the λ DNA is called a prophage and stays resident within the host’s genome without apparent harm to the host. The host is termed a lysogen when a prophage is present.

Why are there higher concentrations of Xis than int in phage?

Higher concentrations of xis than int result in no insertion or excision of phage genomes, the evolutionarily favoured action – leaving any pre-insterted phage genomes inserted (so reducing competition) and preventing the insertion of the phage genome into the genome of a doomed host.

When does the lysogenic life cycle of Lambda begin?

Lysogenic (or lysenogenic) life cycle. The lysogenic lifecycle begins once the cI protein reaches a high enough concentration to activate its promoters, after a small number of infections. The ‘late early’ transcripts continue being written, including xis, int, Q and genes for replication of the lambda genome.

How is lambda DNA replicated in a bacterial cell?

Lambda phage. During infection, the phage particle recognizes and binds to its host, E. coli, causing DNA in the head of the phage to be ejected through the tail into the cytoplasm of the bacterial cell. Usually, a ” lytic cycle ” ensues, where the lambda DNA is replicated and new phage particles are produced within the cell.