Novel Properties of DNA Polymerase β with Poly(rA). oligo(dT) Template-Primer1

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Abstract
Purified DNA polymerase β of calf thymus can utilize poly(rA) oligo(dT) as efficiently as poly(dA).oligo(dT) or activated DNA as a template-primer. The poly(rA) dependent activity of DNA polymerase β was found to differ markedly from the DNA-depend ent activity of the same enzyme (with either activated calf thymus DNA or poly(dA).(dT)10) in the following respects. 1) Poly(rA)-dependent activity was strongly inhibited by natural DNA from various sources or synthetic deoxypolymer duplexes at very low concentrations (less than 0.5 μg/ml) at which the DNA-dependent activity was affected to a much smaller extent, if at all. 2) Poly(rA)-dependent activity was inhibited by N-ethylmaleimide more strongly than DNA-dependent activity measured at 37°C, while it was resistant to this reagent at 26°C. 3) The curves of the activity versus substrate concentration were sigmoidal in the poly(rA)-dependent reaction but hyperbolic in the activated DNA-dependent reaction. A kinetic study suggested that the association of β-enzyme protomers may be required to copy the poly(rA) strand.

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