Purification of a DNA-binding protein from Xenopus laevis unfertilized eggs

Abstract
A DNA-binding protein from Xenopus laevis unfertilized eggs has been purified to apparent homogeneity. It is a heat stable, lysine-rich protein and has a molecular weight corresponding to 8,200 daltons, measured by sodium dodecyl sulphate gel electrophoresis. The protein, which is active in a monomeric form, stimulates DNA polymerase ∝, and binds to single and double stranded DNA. One egg contains about 4 × 1012 molecules (minimum estimate) of the protein; since we calculate that 4 × 108 molecules are sufficient to cover the entire genome (haploid complement), there is much more protein than is needed to cover chromosomal DNA.