title: Bacteriophage T4 head morphogenesis. IV. Comparison of gene 16-, 17-, and 49-defective head structures.
abstract: Defective heads present in extracts of bacteriophage T4 gene 16, 17, or 49 mutant-infected cells have been characterized. All appeared as empty shells when examined by negative-stain electron microscopy and showed essentially the same polypeptide pattern on sodium dodecyl sulfate-acrylamide gels. However, when analyzed by several other methods, gene 16- and 17-defective heads were shown to differ markedly from phage heads present in gene 49-defective extracts. First, the gene 16- and 17-defective structures were found to possess a large number of attached tails (50%, rather than about 5%). Second, they contained less nuclease-resistant deoxyribonucleic acid (DNA) (3 versus 18% of a phage equivalent), had a smaller sedimentation coefficient (240 versus 315S), and a lighter density (1.31 vs. 1.34 g/ml) than gene 49-defective heads. Third, they were not attached to the intracellular DNA pool through a deoxyribonuclease-sensitive linkage. Finally, 8-nm diameter capsomers were clearly revealed on the surface of many gene 16- and 17-defective structures. There was a total of 305 +/- 25 capsomers per particle, which yielded an approximate molecular weight of 84 x 10(6) for these heads. The capsomers were presumably not seen on gene 49-defective heads because of the large amount (18%) of associated DNA. These results support the contention that gene 16- and 17-defective heads, in contrast to gene 49-defective structures, represent abortive rather than intermediate structures in T4 head morphogenesis.
mesh_terms: D002247:Carbon Isotopes; D002499:Centrifugation, Density Gradient; D002501:Centrifugation, Zonal; D003090:Coliphages / Q000032:analysis / Q000254:growth & development; D004279:DNA, Viral / Q000032:analysis; D003673:Defective Viruses; D004591:Electrophoresis, Polyacrylamide Gel; D004926:Escherichia coli; D008040:Genetic Linkage; D005827:Genetics, Microbial; D008854:Microscopy, Electron; D008970:Molecular Weight; D009024:Morphogenesis; D009154:Mutation; D010455:Peptides / Q000032:analysis; D012967:Sodium Dodecyl Sulfate; D013936:Thymidine; D014316:Tritium; D014764:Viral Proteins / Q000032:analysis
chemical_list: D002247:Carbon Isotopes; D004279:DNA, Viral; D010455:Peptides; D014764:Viral Proteins; D014316:Tritium; D012967:Sodium Dodecyl Sulfate; D013936:Thymidine