title: Isolation of a yeast single-strand deoxyribonucleic acid binding protein that specifically stimulates yeast DNA polymerase I.
abstract: 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.
mesh_terms: D004247:DNA / Q000096:biosynthesis; D004265:DNA Helicases / Q000302:isolation & purification*; D004256:DNA Polymerase I / Q000378:metabolism*; D004261:DNA Replication; D004277:DNA, Single-Stranded / Q000378:metabolism*; D004268:DNA-Binding Proteins; D004259:DNA-Directed DNA Polymerase / Q000378:metabolism*; D005656:Fungal Proteins / Q000302:isolation & purification*; D008970:Molecular Weight; D012313:RNA / Q000378:metabolism; D012441:Saccharomyces cerevisiae; D013329:Structure-Activity Relationship
chemical_list: D004277:DNA, Single-Stranded; D004268:DNA-Binding Proteins; D005656:Fungal Proteins; D012313:RNA; D004247:DNA; D004256:DNA Polymerase I; D004259:DNA-Directed DNA Polymerase; D004265:DNA Helicases