Endo/Exo-Nuclease with Type I, II, III
catalyze the hydrolysis of the phosphodiester bond
cut the nucleotides from the middle of DNA or RNA molecules
cut the nucleotides from the ends of DNA and RNA molecules
cannot work on circular DNA
can work on circular DNA
may form blunt ends or sticky ends
form sticky ends
result in oligonucleotide
result in single nucleotide
Type I is an enzyme that has 3 subunits for restricted digestion and methylase activity. It cuts nucleotides at the site away from the recognition site. ATP and S-adenosyl-1-methionine are required to function.
Type II endonuclease means there are two different enzymes, one is to cleave the nucleotides, one is to modify the recognition sequence. They do not use ATP for their activity. It cleaves the sequence at a short specific distance within or from the recognition site.
Type III is a single enzymes that contains two subunits. They cut at a site that is close to the identification site. Same with the type I, they also require ATP.
single-stranded DNA is broke in a 3′ to 5′ direction and releasing deoxyribonucleoside 5′-monophosphates one after another. DNA strands without terminal 3′-hydroxyl groups are not cleaved because they are blocked by a phosphoryl or acetyl group.
Type II exonuclease is associated with DNA polymerase I containing a 5′ exonuclease. The 5′ exonuclease cuts RNA primers directly upstream of the DNA synthesis site in a 5′ to 3′ direction.
Type III exonuclease catalyzes the removal of single nucleotides, one by one, from the 3′-OH end of double-stranded DNA