Structure and function of the major tail protein of bacteriophage lambda: Mutants having small major tail protein molecules in their virion

Viable mutants of bacteriophage lambda having small major tail protein molecules in their virion have been isolated as pseudo-revertants of a defective prophage mutant (defK244) in gene V, which codes for the major tail protein. According to deletion mapping, the defK244 mutation is located near the translation terminal of gene V, whereas some mappable reversion mutations leading to small major tail protein molecules map upstream to defK244 but still downstream to all the amber mutations tested. This suggests (if not proves) that the removable part is located at or near the carboxyl terminal of the major tail protein. Sodium dodecyl sulfate/polyacrylamide gel electrophoresis and buoyant density measurements of the mutant phage particles show that as much as one-third of the major tail protein molecule can be removed without losing its capacity to maintain the total shape and infectivity of the phage particles. In the three-dimensional structure of the tail the removable part of the molecule exists as a protrusion at the outer part of the tail tube according to electron microscopy and hydrodynamic calculations based on sedimentation velocity experiments.