Sulfolobus synthesizes a large quantity of highly conserved 7-kD DNA binding proteins suspected to be involved in chromosomal organization. The effect of the 7-kD proteins on the polymerization and 3’-5’ exonuclease activities of a family B DNA polymerase (polB1) from the hyperthermophilic archaeon Sulfolobus solfataricus was investigated. PolB1 degraded both ssDNA and dsDNA at similar rates in vitro at temperatures of physiological relevance. The 7-kD proteins were capable of significantly inhibiting the excision and enhancing the extension of matched template primers by the polymerase. However, the proteins did not protect ssDNA from cleavage by polB1. In addition, the 7-kD proteins did not affect the proofreading ability of polB1 and were not inhibitory to the excision of mismatched primers by the polymerase. The dNTP concentrations required for the effective inhibition of the 3’-5’ exonuclease activity of polB1 were lowered from ~600 µM in the absence of the 7-kD proteins to ~50 µM in the presence of the proteins at 65 oC. Our data suggest that the 7-kD chromatin proteins serve to modulate the extension and excision activities of the hyperthermophilic DNA polymerase, reducing the cost of proofreading by the enzyme at high temperature.