Iolation and charcterization of a DNA-binding non-histone protein from Tetrahymena pyriformis

Three proteins (A, B and C) that bind specifically to single-stranded DNA have been isolated from the eukaryotic organism Tetrahymena pyriformis. Their molecular weights are 47 000, 41 000 and 32 000. The amino acid composition of the A protein indicates that it is a non-histone protein and sucrose gradient centrifugation shows that it binds to bacteriophage M13 DNA and to oligo (dT)100 in a cooperative manner. The exonucleolytic degradation of oligo (dT)100 is prevented when it is bound to the A protein. The effect of A protein on the exonucleolytic reaction confirms the cooperative manner of binding of A protein binding to oligo (dT)100 and shows that this process may be prevented by high ionic strength. The A protein seems to be without enzymatic activity.