The Structure of the Lambda Particle
The physical structure of lambda phage and the organization of the genetic map of lambda show the same relationship as the physical structure of the ribosome and the organization of the genetic map of ribosomal proteins. The genes for proteins that lie near one another in the particles often lie near one another in the genetic map (Fig. 21.15). Even though a single species of a polycistronic messenger is synthesized that includes all the phage late genes, they are translated at vastly different efficiencies closely paralleling the numbers of the different types of protein molecules that are found in the mature phage particle.
The A protein, often denoted pA, in conjunction with pNu1 is respon-sible for producing the cohesive ends of the DNA. Proteins pD and pE are the major capsid proteins. Protein pE plus Nu3 followed by pB and pC is able to form a precursor of the head, pNu3 is then degraded and pD is added. In the final structure, protein pD is interspersed with equal numbers of protein pE, that is, pD and pE are the two major capsid proteins. Protein pFII as well as protein pW are involved with steps preparing the head assembly for receipt of the tail. pFII provides a specificity for the type of tail that is attached to the head. Protein pV is the major structural protein of the tail. Proteins pH, pM, pL, and pK are all involved in the transition from the tail tube to the tail fibers at the end, which are made from pJ, pTfa, and pStf.
Figure 21.15 The genetic map ofsome genes involved with forming the head and tail of lambda and the locations of the gene products in the physical structure of the head and tail.