The mutational specificity of DNA polymerase-beta during in vitro DNA synthesis. Production of frameshift, base substitution, and deletion mutations.

Abstract:

The frequency and specificity of mutations produced in vitro by eucaryotic DNA polymerase-beta have been determined in a forward mutation assay using a 250-base target sequence in M13mp2 DNA. Homogeneous DNA polymerase-beta, isolated from four different sources, produces mutations at a frequency of 4-6%/single round of gap-filling DNA synthesis. DNA sequence analyses of 460 independent mutants resulting from this error-prone DNA synthesis demonstrate a wide variety of mutational events. Frameshift and base substitutions are made at approximately equal frequency and together comprise about 90% of all mutations. Two mutational "hot spots" for frameshift and base substitution mutations were observed. The characteristics of the mutations at these sites suggest that certain base substitution errors result from dislocation of template bases rather than from direct mispair formation by DNA polymerase-beta. When considering the entire target sequence, single-base frameshift mutations occur primarily in runs of identical bases, usually pyrimidines. The loss of a single base occurs 20-80 times more frequently than single-base additions and much more frequently than the loss of two or more bases. Base substitutions occur at many sites throughout the target, representing a wide spectrum of mispair formations. Averaged over a large number of phenotypically detectable sites, the base substitution error frequency is greater than one mistake for every 5000 bases polymerized. Large deletion mutations are also observed, at a frequency more than 10-fold over background, indicating that purified DNA polymerases alone are capable of producing such deletions. These data are discussed in relation to the physical and kinetic properties of the purified enzymes and with respect to the proposed role for this DNA polymerase in vivo.

Polymerases:

Topics:

Fidelity, Nucleotide Incorporation, Source / Purification

Status:

new topics/pols set partial results complete validated

Results:

Polymerase Reference Property Result Context
Chicken Pol beta Kunkel TA1985 Cloned or native Native organism
Chicken Pol beta Kunkel TA1985 Frameshift Error Rate 0.012 errors/bp Technique: M13mp2 forward mutation assay
Chicken Pol beta Kunkel TA1985 Overall Error Rate 0.035 errors/bp Technique: M13mp2 forward mutation assay
Chicken Pol beta Kunkel TA1985 Nucleotide Substitution Rate 0.019 errors/bp Technique: M13mp2 forward mutation assay
Chicken Pol beta Kunkel TA1985 Full length or truncated Full length
Rat Pol beta Kunkel TA1985 Cloned or native Native organism
Rat Pol beta Kunkel TA1985 Frameshift Error Rate 0.0355 errors/bp Technique: M13mp2 forward mutation assay
Rat Pol beta Kunkel TA1985 Overall Error Rate 0.064 errors/bp Technique: M13mp2 forward mutation assay
Rat Pol beta Kunkel TA1985 Nucleotide Substitution Rate 0.022 errors/bp Technique: M13mp2 forward mutation assay
Rat Pol beta Kunkel TA1985 Full length or truncated Full length
Human Pol beta Kunkel TA1985 Overall Error Rate 0.076 errors/bp Technique: M13mp2 forward mutation assay
Human Pol beta Kunkel TA1985 Gap Filling Yes

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