ASCP MB I B: Molecular Science Polymerases, Exonucleases, Restriction Enzymes

DNA Pol I

- repairs gaps; 3'-5' AND 5'-3' exonuclease activity

- prokaryotic, lagging strand synthesis

DNA Pol II

- gap repair, 3'->5' exonuclease activity

- prokaryotic

DNA pol III holoenzyme

main prokaryotic DNA polymerase for replication; synthesizes leading strand

- 3'->5' exonuclease activity

RNA Pol I

- in nucleolus

- synthesizes rRNA (except 5S rRNA)

RNA Pol II

- in nucleus

- synthesizes mRNAs and snRNAs

RNA Pol III

- in nucleus

- synthesizes tRNAs, 5S rRNA, and some snRNAs

RNA Pol holoenzyme

- subunits α, α, β, β', and σ

- prokaryotic

- transcription initiation

DNA Pol α

- eukaryotic

- primer synthesis

- involved in initiation of DNA replication and has primase activity

- lacks 3' exonuclease activity (for proofreading errors)

DNA pol γ

- replicates mitochondrial DNA (gaMMa)

- eukaryotic

DNA Pol δ

- main enzyme for replication in eukaryotes

- 3'->5' exonuclease activity

DNA Pol ε

- DNA repair (eukaryotic)

- removes primers from lagging strand

DNA Polymerases β λ μ σ

- eukaryotic

- repair

exonuclease I

degrades ssDNA from 3'-->5'

exonuclease III

- removes 5' mononucleotides from 3' end of the dsDNA in the presence of Mg2+ and Mn2+.

- removes nucleotides from blunt ends, recessed ends, and nicks, but NOT overhangs!

exonuclease VII

- degrades ssDNA from either the 5' or 3' end

- one of the few enzymes that has 5' exonuclease activity

Type I restriction enzymes

- single multifunctional enzyme; nuclease + methylase activity

- bind to host-specific DNA sites of 4-6bp separated by 6-8 bp and containing methylated adenines

- cleavage site up to 1000bp from recognition site.

ex: EcoK

Type II restriction enzymes

- used most frequently in the lab

- bind to palindromic DNA recognition sites

- cleave at or near binding site

- sticky or blunt ends

ex: EcoR1, HindII, BamHI

Type III restriction enzymes

- resemble type I enzymes in their ability to methylate and restrict (cut) DNA.

- adenine methylation on only one strand.

- asymmetrical recognition site, cleaves 24-26 bp from that site to the 3' side