Isolation of lambda prophage mutants defective in structural genes: their use for the study of bacteriophage morphogenesis.

Mutants of coliphage lambda defective in structural genes were isolated and characterized. The isolation method consisted in lysogenizing bacteria with mutagenized phage and testing for inability to form plaques after heat induction. The mutants were propagated as prophages in the lysogens. Mutants in the region of the tail-genes U, V, G and H were enriched for by a selection method based on recombination and complementation with known mutants, and they were mapped by deletion mapping with newly isolated lambdadg's. The lysates of all the mutants were examined by electron microscopy. Some of the mutants showed phenotypes different from those of known amber mutants in the same genes. They are interpreted as producing partially active, altered gene products and might be useful for the studies of morphogenesis and of the mechanism of infection.