User:Natpollock/Integration host factor

Rightward transcription expresses the O, P and Q genes. O and P are responsible for initiating replication, and Q is another antiterminator that allows the expression of head, tail, and lysis genes from P_R’.

Pr is the promoter for rightward transcription, and the cro gene is a regulator gene. The cro gene will encode for the Cro protein that will then repress Prm promoter.  Once Pr transcription is underway the Q gene will then be transcribed at the far end of the operon for rightward transcription. The Q gene is a regulator gene found on this operon, which will control the expression of later genes for rightward transcription. Once the gene's regulatory proteins allow for expression, the Q protein will then act as an anti-terminator. This will then allow for the rest of the operon to be read through until it reaches the transcription terminator. Thus allowing expression of later genes in the operon, and leading to the expression of the lytic cycle.

Pr promoter has been found to activate the origin in the use of rightward transcription, but the whole picture of this is still somewhat misunderstood. Given there are some caveats to this, for instance this process is different for other phages such as N15 phage, which may encode for DNA polymerase. Another example is the P22 phage may replace the p gene, which encodes for an essential replication protein for something that is capable of encoding for a DnaB helices..

Leftward transcription

1. Lambda phage inserts chromosome into the cytoplasm of the host bacterial cell.
2. The phage chromosome is inserted to the host bacterial chromosome through DNA ligase.
3. Transcription of the phage chromosome proceeds leftward when the host RNA polymerase attaches to promotor site pL resulting in the translation of gene N.
   1. Gene N acts a regulatory gene that results in RNA polymerase to be unable to recognize translation-termination sites.

Leftward Transcription Mutations

Leftward transcription is believed to result in a deletion mutation of the rap gene resulting in a lack of growth of lambda phage. This is due to RNA polymerase attaching to pL promoter site instead of the pR promotor site. Leftward transcription results in barI and barII transcription on the left operon. Bar positive phenotype is present when the rap gene is absent. The lack of growth of lambda phage is believed to occur due to a temperature sensitivity resulting in inhibition of growth.

Leftward transcription expresses the gam, xis, bar and int genes. Gam proteins are involved in recombination. Gam is also important in that it inhibits the host RecBCD nuclease from degrading the 3’ ends in rolling circle replication. Int and xis are integration and excision proteins vital to lysogeny.

As a genetic tool

Lambda phage has been used heavily as a model organism and has been an excellent tool first in microbial genetics, and then later in molecular genetics. Some of its uses include its application as a vector for the cloning of recombinant DNA; the use of its site-specific recombinase (int) for the shuffling of cloned DNAs by the gateway method; and the application of its Red operon, including the proteins Red alpha (also called 'exo'), beta and gamma in the DNA engineering method called recombineering. The 48 kb DNA fragment of lambda phage is not essential for productive infection and can be replaced by foreign DNA, which can then be replicated by the phage. Lambda phage will enter bacteria more easily than plasmids, making it a useful vector that can either destroy or become part of the host's DNA. Lambda phage can also be manipulated and used as an anti-cancer vaccine that targets human aspartyl (asparaginyl) β-hydroxylase (ASPH, HAAH), which has been shown to be beneficial in cases of hepatocellular carcinoma in mice . Lambda phage has also been of major importance in the study of specialized transduction.

Nat doing this part^

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