DNA Polymerase I

Product Description

DNA Polymerase I is a mesophilic DNA polymerase that exhibits 5′-3′ DNA synthesis in addition to both 3′→ 5′ and 5′→ 3′ exonuclease activities. The combination of DNA synthesis and 5′→ 3′ nuclease characteristics enable nick-translation during DNA synthesis.

Source of Protein
A recombinant E. coli strain carrying the PolA gene.

Supplied in 
25 mM Tris-HCl
0.1 mM EDTA
1.0 mM DTT
50% glycerol
pH 7.4 @ 25°C

Supplied With
B0110 (10X Blue Buffer)

10X Blue Buffer (B0110)
500 mM NaCl
100 mM Tris-HCl
100 mM MgCl₂
10 mM DTT
pH 7.9 @ 25°C

Unit Definition
1 unit is defined as the amount of polymerase required to convert 10 nmol of dNTPs into acid insoluble material in 30 minutes at 37°C.

Quality Control Analysis

Unit Characterization Assay
Unit activity was measured using a 2-fold serial dilution method. Dilutions of enzyme were made in 1X Blue Reaction Buffer and added to 50 µL reactions containing Calf Thymus DNA, 1X Blue Reaction Buffer, 3H-dTTP and 100 µM dNTPs. Reactions were incubated 10 minutes at 37°C, plunged on ice, and analyzed using a TCA-precipitation method.

Protein Concentration (OD₂₈₀) Measurement
A 2.0 µL sample of enzyme was analyzed at OD₂₈₀ using a Nanodrop ND-1000 spectrophotometer standardized using a 2.0 mg/ml BSA sample (Pierce Cat #23209) and blanked with product storage solution. The observed average measurement of 3 replicate samples was converted to mg/mL using an extinction coefficient of 80,790 and molecular weight of 103,118 Daltons.

SDS-Page (Physical Purity Assessment)
2.0 µL of concentrated enzyme solution was loaded on a denaturing 4-20% Tris-Glycine SDS-PAGE gel flanked by a broad-range MW marker and 2.0 µL of a 1:100 dilution of the sample. Following electrophoresis, the gel was stained and the samples compared to determine physical purity. The acceptance criteria for this test requires that the aggregate mass of contaminant bands in the concentrated sample do not exceed the mass of the protein of interest band in the dilute sample, confirming greater than 99% purity of the concentrated sample.

Contamination Tests

Single-Stranded Exonuclease Activity
A 50 µL reaction containing 10,000 cpm of a radiolabeled single-stranded DNA substrate and 10 µL of enzyme solution incubated for 4 hours at 37°C resulted in greater than 80% release of TCA-soluble counts.

Double-Stranded Exonuclease Activity
A 50 µL reaction containing 5,000 cpm of a radiolabeled double-stranded DNA substrate and 10 µL of enzyme solution incubated for 4 hours at 37°C resulted in greater than 50% release of TCA-soluble counts.

Double-Stranded Endonuclease Activity
A 50 µL reaction containing 0.5 µg of pBR322 DNA and 10 µL of enzyme solution incubated for 4 hours at 37°C resulted in no visually discernible conversion to nicked circular DNA as determined by agarose gel electrophoresis.

E.coli 16S rDNA Contamination Test
Replicate 5 µL samples of enzyme solution were denatured and screened in a TaqMan qPCR assay for the presence of contaminating E.coli genomic DNA using oligonucleotide primers corresponding to the 16S rRNA locus. The acceptance criterion for the test is the threshold cycle count (C_t) produced by the average of 3 replicate no template control samples. Based on the correlation between the no template control C_t values, and standard curve data, the detection limit of this assay is <10 copies genome/sample.