The problem of how biological structures grow to their correct shape and size is of major importance to cell function and development, but the mechanisms of size regulation at the molecular level are poorly understood. Knowledge of the principles of viral morphogenesis is valuable both for medical control of viral multiplication and for understanding cellular function. The goal of the studies proposed here is to extend our knowledge of the structure and assembly of the tail of bacteriophage T4 with the aim of understanding the mechanisms which regulate the length of this structure that delivers the viral DNA into the host cell. The complete baseplate, with gp 48 and gp 54 added, permits the binding of tail tube protein gp 19. Tail length is regulated by the completed baseplate and we suspect that gp 48 may be the "ruler" molecule that determines length. We will insert T4 genes 19, 48 and 54 in appropriate vectors in E. coli, characterize the cloned DNA, insert the DNA in M13 vectors, determine DNA sequences, and analyze and compare predicted protein sequences for each gene. We will analyze the sequences for hydrophobicity repeat features, and possible contact regions. We will produce quantities of gp 48 in expression-overproducing vectors, purify gp 48, prepare anti-gp 48 IgG, and localize gp 48 on baseplates and "core + fiber" structures. We also plan to modify the gp 48 to test the ruler hypothesis: internal, in-phase deletions will be prepared, and we will insert duplications of 1-200 bp to extend the protein. We will produce amino acid substitutions at several defined sites, all with the goal of testing the modified gp 48 for altered tube length assembly. We will try to answer the question of whether the growing tube has exposed gp 48; by generating intermediates and characterizing them by electron microscopy. Also, since a terminator protein is necessary in phage lambda for tail length limitation, we think that T4 gp 3 may be involved in length regulation. We will characterize gene 3 mutations by genetic analysis, localize gp 3, determine its molecular weight and aggregate size, measure the excess (if any) of gp 3 in infected cells by gene dosage, and stabilize the tail length distribution in vitro by adding gp 3 to assembly mixtures.