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D. W. Bath 《Experimental cell research》1976,98(2):262-268
The surface ultrastructure of trypsin-banded chromosomes has been examined by electron microscopy. Trypsin pretreatment removed cellular debris and produced banding patterns recognizable with the electron microscope as ridges in platinum-carbon replicas. The ridges observed in replicas of trypsin-treated chromosomes corresponds to Giemsa-stained bands observed by light microscopy. The bands appeared as an area of tightly compacted fibrils on the surface of the chromosomes. Prolonged treatment in trypsin resulted in collapsed chromosomes and loss of ridges in the replicas. Interchromosomal fibers were also noted and in some preparations appeared to be localized to banded regions. 相似文献
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Bilcock DT Daniels LE Bath AJ Halford SE 《The Journal of biological chemistry》1999,274(51):36379-36386
Type II restriction endonucleases usually recognize 4-6-base pair (bp) sites on DNA and cleave each site in a separate reaction. A few type II endonucleases have 8-bp recognition sites, but these seem unsuited for restriction, since their sites are rare on most DNA. Moreover, only one endonuclease that recognizes a target containing 8 bp has been examined to date, and this enzyme, SfiI, needs two copies of this site for its DNA cleavage reaction. In this study, several endonucleases with 8-bp sites were tested on plasmids that have either one or two copies of the relevant sequence to determine if they also need two sites. SgfI, SrfI, FseI, PacI, PmeI, Sse8781I, and SdaI all acted through equal and independent reactions at each site. AscI cleaved the DNA with one site at the same rate as that with two sites but acted processively on the latter. In contrast, SgrAI showed a marked preference for the plasmid with two sites and cleaved both sites on this DNA in a concerted manner, like SfiI. Endonucleases that require two copies of an 8-bp sequence may be widespread in nature, where, despite this seemingly inappropriate requirement, they may function in DNA restriction. 相似文献
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Mary L. Bath 《PloS one》2010,5(2)