Mechanism of Bacteriophage Lambda Genome Ejection
Authors:Yan Jin, Xiao xue Zhang
- William Gelbart, Professor of Physical chemistry, University of California Los Angeles
- Charles Knobler , Professor Emeritus of Physical chemistry, University of California Los Angeles
Prevention of viral infections requires an understanding of the viral genome ejection mechanism. We investigated lambda bacteriophage, a DNA virus similar to herpes simplex but better characterized and safer to handle. Recent in vitro experiments with lambda have shown that ejection of its genome is driven by high pressure in the viral capsid, and that only half the genome is ejected before the capsid pressure equals the host osmotic pressure. These facts raise the question: what physical mechanism drives the delivery in vivo of the remainder of the genome? An in vitro experiment was designed to test if transcription of the injected half of the genome leads to pulling out of the rest. First, we purified E. coli membrane receptor LamB, lambda phage, and lambda-encoded antiterminator protein N, the only lambda gene transcribed by E. coli RNA polymerase in the absence of viral gene products and whose transcription is towards the phage capsid. Also, we found that transcription yields of short DNA are only weakly dependent on polyethylene glycol (PEG) used to mimic cytoplasm pressure. Lambda phage, LamB and PEG will be flowed into the space between two cover slips under a fluorescence microscope to trigger and observe the partial ejection of lambda genome. To test our hypothesis that transcription of N drives genome delivery, the length of genome ejected will be measured before and after transcription with and without protein N.