The Rex system of bacteriophage lambda: tolerance and altruistic cell death

Area of Science:

• Microbiology
• Molecular Biology
• Virology

Background:

• Bacteriophage lambda possesses a two-component Rex system (RexA and RexB) that inhibits the lytic development of other bacterial viruses.
• This Rex exclusion mechanism leads to the cessation of macromolecular synthesis, impaired active transport, ATP hydrolysis, and ultimately cell death.

Purpose of the Study:

• To investigate the intracellular localization and membrane topology of the RexB protein.
• To elucidate the mechanism by which the Rex system causes cell death and how bacteriophage lambda avoids self-exclusion.

Main Methods:

• Cell fractionation was employed to determine the location of the RexB protein within the cell.
• RexB-alkaline phosphatase fusions were constructed to analyze the membrane topology of RexB.
• Experiments involving overexpression of RexB in lambda lysogens were conducted to assess its role in preventing self-exclusion.

Main Results:

• The RexB protein was identified as a polytopic transmembrane protein, suggesting it forms ion channels.
• These channels likely depolarize the cytoplasmic membrane, leading to the observed effects of Rex exclusion.
• Overexpression of RexB in lambda lysogens successfully prevented the exclusion of T4 rII mutants and lambda ren mutants.

Conclusions:

• The RexB protein functions as an ion channel, mediating membrane depolarization during bacteriophage lambda's lytic cycle.
• Overexpression of RexB is proposed as the mechanism by which lambda prevents its own exclusion, likely through transcriptional regulation.