Sequence-specific single-stranded cuts

Nucleosomes protect DNA from nucleases to differing extents, depending on the nucleases and how closely the nucleosomes are packed together. Deoxyri-bonuclease-I (DNAase-I or DNAse-I) is a nuclease that makes single-stranded cuts in DNA with little sequence specificity and eventually reduces a naked DNA molecule to mono- or small oligonucleotides. 

Attempts are being made to design semisynthetic restriction endonucleases specific for single-stranded DNA or RNA. For example, an oligonucleotide with a sequence complementary to a sequence adjacent the linkage that is to be cut can be covalently linked to a relatively nonspecific nuclease. Such an enzyme derived from micrococal nuclease cuts a single-stranded chain of either DNA or RNA adjacent to the double-stranded region of the ES complex.839... 

Type II restriction endonucleases (25) are enzymes isolated from procaryotes which recognize and make double-stranded cuts at specific DNA sequences. We investigated how platination of plasmid pBR322 would affect the ability of the enzyme Bam HI to cut at its single recognition sequence in this plasmid (23) Bam HI... 

A FIGURE 9-10 Cleavage of DNA by the restriction enzyme EcoRI. This restriction enzyme from coli makes staggered cuts at the specific 6-bp inverted repeat (palindromic) sequence shown, yielding fragments with single-stranded, complementary "sticky" ends. Many other restriction enzymes also produce fragments with sticky ends. 

Restriction enzymes (endonucleases) typically cut DNA at specific 4- to 8-bp palindromic sequences, producing defined fragments that often have self-complementary single-stranded tails (sticky ends). 

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