Isolation of a yeast single-strand deoxyribonucleic acid binding protein that specifically stimulates yeast DNA polymerase I

Biochemistry. 1983 Jun 21;22(13):3214-9. doi: 10.1021/bi00282a027.


We sought a protein from yeast that would bind more strongly to single-stranded DNA than to duplex DNA and would stimulate the activity of the major yeast DNA polymerase, but not polymerases from other organisms. We isolated a protein that binds about 200 times more strongly to single-stranded DNA than duplex DNA and stimulates yeast DNA polymerase I activity 4-5-fold. It inhibits synthesis catalyzed by calf thymus DNA polymerase alpha and has little effect on T4 DNA polymerase. This yeast protein, SSB-1, has a molecular weight of approximately 40 000. At apparent saturation there is one protein molecule bound per 40 nucleotides. Protein binding causes the single-stranded DNA molecule to assume a relatively extended conformation. It binds to single-stranded RNA as strongly as to DNA. SSB-1 increases the initial rate of polymerization catalyzed by yeast DNA polymerase I apparently by increasing the processivity of the enzyme. We estimate there are 7500-30 000 molecules of SSB-1 per yeast cell, enough to bind at least 400-1600 nucleotides per replication fork. Thus it is present in sufficient abundance to participate in DNA replication in vivo in the manner suggested by these in vitro experiments.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • DNA / biosynthesis
  • DNA Helicases / isolation & purification*
  • DNA Polymerase I / metabolism*
  • DNA Replication*
  • DNA, Single-Stranded / metabolism*
  • DNA-Binding Proteins
  • DNA-Directed DNA Polymerase / metabolism*
  • Fungal Proteins / isolation & purification*
  • Molecular Weight
  • RNA / metabolism
  • Saccharomyces cerevisiae
  • Structure-Activity Relationship


  • DNA, Single-Stranded
  • DNA-Binding Proteins
  • Fungal Proteins
  • RNA
  • DNA
  • DNA Polymerase I
  • DNA-Directed DNA Polymerase
  • DNA Helicases