12 Exodeoxyribonucleases of Escherichia coli

摘要: Publisher Summary Deoxyribonucleases (DNases) catalyze the hydrolysis of phosphodiester bonds in polydeoxyribonucleotides. They are divided into two classes—namely, (1) exonucleases and (2) endonucleases. Essentially, an endonuclease can attack a covalently closed circular strand, but exonuclease cannot because it requires chain terminus. Also, if preparation is contaminated with small amount endonuclease, capable rapidly degrading DNA molecules. This chapter describes E.coli emphasis on classes I, III, IV, VII, VIII. all cleave to produce 5′-rather than 3′-phosphomonoesters. In cases where directionality enzyme known, always at least 3′ → 5′. Some enzymes have, addition, 5′→3′ activity. Exonuclease I 3′→ 5′ that specific for single-stranded DNA. It attacks strand processively releasing 5′-mononucleotides, down its 5′-terminal dinucleotide, which leaves intact. The usually assayed by measuring degradation radiolabeled, heat-denatured acid-soluble products. III monomeric protein four catalytic activities—namely, bihelical DNA, RNA RNA–DNA hybrid duplex (RNase H activity), (3) 3′-terminal phosphomonoesters from (DNA-3′-phosphatase (4) cleavage endonucleolytically apurinic or apyrimidinic site (AP activity) creating base-free deoxyribose 5-phosphate end groups.