The product of the bacteriophage lambda W gene: purification and properties.

Gene W is one of the 10 genes that control the morphogenesis of the bacteriophage lambda head. The morpho genesis of the phage lambda head proceeds through the synthesis of an intermediate assembly called the prohead. This is an empty shell into which the bacteriophage DNA is introduced--packaged--by the phage enzyme DNA terminase. The product of W (gpW) acts after DNA packaging, but before the addition of another phage product, gene product FII, and before the addition of tails. The role of gpW is unknown. The structure of N- and C-tagged gpW has been previously determined by nuclear magnetic resonance (NMR) spectroscopy. Here we report some of the properties of the native protein. The purification of gpW to homogeneity, overproduced by a plasmid derivative, is described. To obtain large amounts of the protein, the ribosome-binding site had to be modified, showing that inefficient translation of the message is the main mechanism limiting W gene expression. The molecular weight of the protein is in close agreement to the value predicted from the DNA sequence of the gene, which suggests that it is not post-transcriptionally modified. It behaves as a monomer in solution. Radioactively labeled gpW is incorporated into phage particles in in vitro complementation, showing that gpW is a structural protein. The stage at which gpW functions and other circumstantial evidence support the idea that six molecules of gpW polymerize on the connector before the incorporation of six molecules of gpFII and before the tail attaches.

The solution structure of the bacteriophage lambda head-tail joining protein, gpFII.

The bacteriophage lambda FII protein (gpFII) is a 117 residue structural protein found in the phage particle that is required for the joining of phage heads and tails at the last step of morphogenesis. We have performed biophysical experiments to show that gpFII is stable, monomeric, and reversibly folded. We have also determined the atomic resolution structure of gpFII using NMR spectroscopy. gpFII is shown to possess a novel fold consisting of seven beta-strands and a short alpha-helix. It also displays two large unstructured regions at the N terminus (residues 1-24) and in a large loop near the middle of the protein (residues 46-62). We speculate that these unstructured regions become structured when gpFII assembles into the phage particle, and that these conformational changes play an important role in regulating the assembly pathway. Alignment of the gpFII sequence with those of homologues from other lambdoid phages has allowed us to putatively identify distinct surfaces on the gpFII structure that mediate binding to the phage head and tail.