Isolation of the Bacteriophage Lambda A

An in vitro assay for measuring the activity of the phage X A-gene product has been developed. The assay is based on the observation that A-donor extracts complement A- extracts for packaging of exogenous im- mature X DNA into phage particles. A partial purification of the A-gene product activity using this assay is pre- sented. A method is suggested by which this A protein- dependent in vitro system might be manipulated to analyze the mechanism of reforming the X cohesive ter- mini during chromosome assimilation into phage pre- cursors.