Assembly of phage lambda in vitro.

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Abstract
The results of in vitro complementation tests involving lysates of mutants of lambda defective in 12 of the 13 genes concerned with virus morphogenesis reveal but two complementing types. Lysates of the mutants A through E complement with lysates of mutants G through M to form active phage particles. The mutants G through M contribute the genome already contained in head membranes. The mutants A through E presumably contribute the tail. In the terminology of Edgar and Wood, mutants A through E are tail donors and G through M head donors. These conclusions are supported by sedimentation experiments in sucrose gradients showing that the activity in the lysates A through E sediments with a velocity expected for tails, while the activity in G through M lysates sediments with a velocity expected for heads without tails. Genes A through E seem to be concerned with head formation so that defective lysates contain tails but no heads, while genes G through M are concerned with tail formation so that defective lysates contain heads but no tails. It is probable that in vitro the heads and tails can unite spontaneously to form active phage particles.