PubMed · 13022106
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1952. CONDENSED, M.B.B.S. course.. https://pubmed.ncbi.nlm.nih.gov/13022106/
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Bacterial viruses (bacteriophages) consist of nucleic acid protected by a protein envelope called capsid. At the start of infection, the phage genome is translocated into the bacterial cytoplasm. In vitro (and also in vivo), this DNA release can be triggered by binding a specific receptor protein to the phage tail. The force responsible for the release arises from energy stored in the capsid due to strong confinement of the DNA. We show that this force can be modified by adding molecules like spermine that affect DNA conformation. The tetravalent cation spermine can reduce the pressure inside the capsid and induce condensation of the released DNA. We examine the effect of spermine on DNA ejection from phage T5 by using light scattering and gel electrophoresis to measure the amount of DNA remaining in the capsid at the end of ejection. We discuss the results in terms of free energy minimization and we demonstrate that the presence of a DNA condensate outside the phage generates an additional force pulling passively on the DNA remaining inside the capsid.
Past strategies for the analysis of ATP-fueled motors include single-motor analysis. Single-motor analysis bypasses limitations caused by motor asynchrony during the traditional ensemble averaging analysis. The present communication describes revised ensemble averaging analysis that also can bypass asynchrony-derived limitations. This revised analysis makes measurements of one motor variable dependent on the others. One example is nondenaturing gel electrophoresis with more than one dimension. Each dimension measures one of the motor variables. This multidimensional procedure is used to obtain the values of "conformational" motor variables as a function of a "clock" motor variable. In theory, the cycle of the motor can be analyzed from a single multidimensional analysis of a collection of asynchronous motors sampled at only one time. That is to say, motor asynchrony becomes an asset, rather than a liability.
The abundant presence of temperate phages in the chromosomes of clinical isolates of Streptococcus pneumoniae has been well documented. The genome of MM1, a temperate phage of pneumococcus, has been isolated as a DNA-protein complex. The protein is covalently bound to the DNA, was iodinated in vitro with Na125I, and has an Mr of 22,000. Electron microscopy and enzymatic analyses revealed that the MM1 genome is a linear, circularly permuted, terminally redundant collection of double-stranded DNA molecules packaged via a headful mechanism. The location of the pac site appears to be downstream of the terminase, between orf32 and orf34 of the MM1 genome.