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Morphogenetic structures present in lysates of amber mutants of bacteriophage Mu
Abstract:
The Mu phage particle is structurally similar to that of the T-even phages, consisting of an icosahedral head and contractile tail. This study continues an analysis of the morphogenesis of the Mu phage particle by defining the structural defects resulting from mutations in specific Mu genes. Defective lysates produced by induction of 55 amber mutants, representing 24 essential genes, were examined in the electron microscope and categorized into eight classes based on the observed phage-related structures. (1) Mutations in genes lys, F and G, and some H mutations, did not cause a visible alteration in particle structure. (2) Mutants defective in genes A, B, and C produced no detectable phage structures, consistent with their lack of production of late RNA. (3) Extracts defective in genes L, M, Y, N, P, Q, V, W, and R contained only head structures, and these appeared normal. (4) K-defective mutants accumulated free heads as well as free tails which were longer than normal and variable in length. (5) Tails which appeared normal were the only structures found in T- and some I-defective extracts. (6) Free tails and empty heads accumulated in D-, E-, and some I- and H-defective extracts. These heads were as much as 16% smaller than normal heads. The heads found in some I amber lysates had a protruding neck-like structure and unusually thick shells suggestive of a scaffolding-like structure. (7) Defects in gene J resulted in the accumulation of unattached tails and full heads. (8) Previous analysis of lysates produced by inversion-defective gin mutants fixed in the G(+) orientation demonstrated that S and U mutants produced particles lacking tail fibers (F.J. Grundy and M.M. Howe (1984), Virology 134, 296-317). In these experiments with Gin+ phages S and U mutants produced apparently normal phage particles. Presumably the tail fiber defects were masked by the production of S' and U' proteins by G(-) phages in the population.
Insights
Investigating Mu phage gene mutations reveals distinct structural defects in phage particle assembly. Understanding these defects is crucial for comprehending phage morphogenesis and developing targeted interventions.
Area of Science:
- Bacteriophage biology
- Molecular genetics
- Structural biology
Background:
- Bacteriophage Mu is structurally similar to T-even phages, possessing an icosahedral head and contractile tail.
- Phage morphogenesis involves complex assembly processes governed by specific viral genes.
Purpose of the Study:
- To elucidate the roles of specific Mu phage genes in particle morphogenesis.
- To characterize structural defects in Mu phage assembly caused by amber mutations.
Main Methods:
- Electron microscopy was used to examine phage-related structures in defective lysates from 55 amber mutants.
- Mutants were categorized into eight classes based on observed structural abnormalities.
Main Results:
- Mutations in different genes resulted in distinct assembly defects, including absence of structures, accumulation of heads or tails, and abnormal head/tail morphology.
- Specific gene defects led to the accumulation of normal or abnormal head and tail structures, or complete lack of phage particles.
- Some mutations affected head size, shell thickness, or neck structure, suggesting roles in scaffolding or structural integrity.
Conclusions:
- The study identified specific Mu phage genes essential for proper head and tail assembly.
- Different gene mutations lead to unique, classifiable defects in phage particle morphogenesis.
- These findings contribute to a detailed understanding of the molecular mechanisms underlying bacteriophage assembly.