Overproduction of bacteriophage Q beta maturation (A2) protein leads to cell lysis.

Double-stranded cDNA from the maturation (or A2) protein gene of the RNA bacteriophage Q beta has been cloned such that its expression is regulated by the E. coli lac promoter/operator. Induction of the A2 clone is lethal to the host. The basis of this lethality is cell lysis, which is correlated with synthesis of the A2 protein. No other major proteins appear to be made from the A2 gene when inducer is added. Plasmid-derived A2 protein specifically complements infecting Q beta A2 amber mutants. Lysis activity is abolished in clones that synthesize truncated or internally deleted A2 polypeptides ranging from 10% to 95% of the length of wild-type protein. We conclude that host lysis is promoted by the maturation protein itself, rather than by a separate lysis protein. The A2 protein probably allows for the release of progeny Q beta phage particles following normal infection.