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111.
112.
Molecular evolution of bacteriophages: evidence of selection against the recognition sites of host restriction enzymes 总被引:12,自引:0,他引:12
Restriction enzymes produced by bacteria serve as a defense against
invading bacteriophages, and so phages without other protection would be
expected to undergo selection to eliminate recognition sites for these
enzymes from their genomes. The observed frequencies of all restriction
sites in the genomes of all completely sequenced DNA phages (T7, lambda,
phi X174, G4, M13, f1, fd, and IKe) have been compared to expected
frequencies derived from trinucleotide frequencies. Attention was focused
on 6-base palindromes since they comprise the typical recognition sites for
type II restriction enzymes. All of these coliphages, with the exception of
lambda and G4, exhibit significant avoidance of the particular sequences
that are enterobacterial restriction sites. As expected, the sequenced
fraction of the genome of phi 29, a Bacillus subtilis phage, lacks Bacillus
restriction sites. By contrast, the RNA phage MS2, several viruses that
infect eukaryotes (EBV, adenovirus, papilloma, and SV40), and three
mitochondrial genomes (human, mouse, and cow) were found not to lack
restriction sites. Because the particular palindromes avoided correspond
closely with the recognition sites for host enzymes and because other
viruses and small genomes do not show this avoidance, it is concluded that
the effect indeed results from natural selection.
相似文献
113.
114.
Diffusion artificats in 3,3'-diaminobenzidine cytochemistry 总被引:14,自引:0,他引:14
115.
A B Novikoff 《The journal of histochemistry and cytochemistry》1967,15(6):353-354
116.
Increasingly, physiological and biochemical data on the mammalian cornea have emphasized the importance of the endothelial rather than the epithelial layer in regulating the state of hydration of the cornea, via a transport ATPase. This view is supported by the observations reported here. With the Ernst method, the first cytochemical procedure to be readily responsive to ions and ouabain, the major sites of enzyme reaction product are the intercellular spaces of the endothelial layer. This localization was not found by us with the so-called ATPase method of Wachstein and Meisel. 相似文献
117.
118.
Microperoxisomes 总被引:9,自引:0,他引:9
119.
A B Novikoff 《The journal of histochemistry and cytochemistry》1970,18(5):366-367
120.