IGEM:Caltech/2007/Project Overview/Q

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Background Information

Q is a 207 amino acid protein with a mostly linear structure. It binds to lambda genomic DNA at qut, then modifies RNA polymerase as it initializes transcription at pR', slightly downstream of Q. This modification causes the RNA polymerase to transcribe genes beyond the terminator tR'.

Role in Lambda Life Cycle

Since it is located downstream of the terminator tR, its transcription requires the presence of N, which causes RNA polymerase to ignore the termination signal. During early stages of lambda phage's life cycle as well as the lysogenic pathway, the translation of Q is downregulated by the promoter pAQ, which transcribes Q in reverse, producing a Q-antisense RNA which binds to Q messenger RNA and prevents ribosomal attachment. Furthermore, a relatively high concentration of Q is required to effectively cause antitermination, giving the phage time to begin a lysogenic life cycle if conditions are appropriate.

Once Q has modified the RNA polymerase, the polymerase begins to transcribe genes beyond tR'. These genes are crucial to the production of new phage components, such as tails and heads (protein capsules). Once these genes are expressed, the phage is committed to the lytic pathway.

Subproject Goals

The goal of this subproject is to determine the approximate concentration of Q necessary to effectively switch from a lysogenic to a lytic pathway. Q amber mutants, which are deficient in the production of Q, will be used, and the production of Q in the host cell will be controlled by varying the concentration of inducer ATC. The fraction of colonies that lyse will be measured, and a graph of lysis vs. Q production will be obtained.