Deoxyribonuclease base specificity

All of the bacterial deoxyribonucleases that have been examined in detail possess a specificity directed in varying degrees toward the secondary structure of the polydeoxynucleotide. With one recent exception, none of the deoxyribonucleases shows a simple base specificity whereby they attack phosphodiester bonds adjacent to a single base. However, it is now clear that several of the endonucleases may possess an extremely high order of specificity and have the capacity to recognize and attack one or a few phosphodiester bonds in polydeoxynucleotide chains composed of many thousands of internucleotide linkages. 

Enzymes catalyzing cleavage of DNA, including endo-deoxyribonucleases that generate 5 -phosphomono-esters [EC 3.1.21.x], endodeoxyribonucleases that produce products other than 5 -phosphomonoesters [EC 3.1.22.x], site-specific endodeoxyribonucleases acting on altered bases [EC 3.1.25.x], and exodeoxyribonucleases producing 5 -phosphomonoesters [EC 3.1.11.x]. A few examples are ... 

During the past decade a previously accepted notion that the deoxyribonucleic acid (DNA)-deoxyribonuclease (DNase I) reaction runs a uniform course with a uniform specificity began to be seriously doubted. It is now realized that striking differences exist between the early and terminal stages of the same reaction. The observed differences are not limited solely to the rate of the reaction but include variations in endo-or exonucleolytic character, in the effect of the divalent cation, and, finally, in the specificity toward the bases adjacent to the bond that is cleaved. 

A variety of enzymes break phosphodiester bonds in nucleic acids deoxyribonucleases (DNases) cleave DNA and ribonucleases (RNases) cleave RNA. DNases usually are specific for single- or double-stranded DNA although some DNases can cleave both. DNases can act as exonucleases in which they remove one nucleotide at a time from either the 3 or 5 end of the strand. Other DNases function as endonucleases and are specific for cleaving between particular pairs of bases. 

Certain deoxyribonucleases cleave any sequence of single-strand DNA to yield nucleoside monophosphates these enzymes do not hydrolyze base-paired DNA sequences. What products would you expect when you incubate a solution containing a singlestrand specific deoxyribonuclease and the follotving oligodeoxyribonucleotide ... 

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