What is transcriptional regulation in lambda bacteriophage?
Gene Transcription Regulation of Phage λ It utilizes two separate mechanisms to regulate early and late transcripts. Expression of early genes is regulated by the phage encoded N-protein that forms a termination-resistant RNAP complex.
What does lambda repressor bind?
Lambda Repressor The repressor molecule of the Lambda bacteriophage binds not only to the OR1 site to prevent Cro transcription, but also to OR2, where it aids the binding of RNA polymerase to the repressor promoter.
What is the site on bacterial DNA required for integration of lambda phage DNA?
Bacterial DNA has an attachment sequence called attB. Bacterial DNA and λ-phage DNA align at the “O” region of the attachment sequences. During integration, int protein induces two double-stranded breaks that are resolved, resulting in the integration of the phage DNA into the bacterial DNA.
What is a COS site?
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.
How long is the lytic cycle?
In wild-type lambda, lysis occurs at about 50 min, releasing approximately 100 completed virions. The timing of lysis is determined by the holin and antiholin proteins, with the latter inhibiting the former.
What does the CRO protein do?
Cro, a repressor protein of temperate bacteriophages (e.g. lambda [l], 434, P22), works in opposition to the phage’s repressor to control the genetic switch that determines whether a lytic or lysogenic cycle will follow infection.
What is the role of phage cl gene?
The phage is maintained in this prophage state through the action of a repressor protein, coded for by the phage gene cl. This repressor protein turns off the expression of virtually the whole of the lambda genome. This leads to the excision of lambda DNA from the host chromosome and entry into the lytic cycle.
Which proteins recognize cos site of lambda DNA?
The DNA passes through the mannose permease complex in the inner membrane (encoded by the manXYZ genes) and immediately circularises using the cos sites, 12-base G-C-rich cohesive “sticky ends”. The single-strand viral DNA ends are ligated by host DNA ligase.
How does phage lambda repress transcription?
Phage lambda, which has been most intensively studied, carries a single gene, cI, that encodes a repressor protein. In a stable lysogenic state, this protein binds to certain sites in the lambda genome and represses transcription of all other lambda genes.
What is lambda phage integration and excision?
A newer cloning system uses the lambda phage integration and excision sites for cloning genes from one vector to another (Fig. 3.27 ). Lambda phage exists as a phage but also integrates into the E. coli chromosome at the attB site to form a prophage.
How does cooperative binding to the lambda repressor work?
The cooperative binding induces repression of the cro gene and simultaneous activation of the cI gene, which code for proteins Cro and cI, respectively (Stayrook et. al, 2008). The Lambda Repressor homodimer is composed of two identical polypeptide chains of 236 amino acid residues.
How many nucleotides are in the lambda phage linear dsDNA genome?
The lambda phage linear dsDNA genome contains 48,490 bp with 12 nucleotide single-stranded segments called “ cos ” sites at the 5′ ends; they help in the circularization of phage DNA before replication in the host cytoplasm.