Purification by DNA-cellulose chromatography of acid-soluble DNA-binding proteins (ASB) from Strepromyces hygroscopicus IS described. Two main fractions, ASBII and ASBIII, containing different major protein components were isolated. The dominating protein of ASBIII (19 kd) could be enriched on Srrepiomyces DNA-cellulose.
DNA-binding properties of ASBIII were studied by using a filter retention assay, thermal melting, and by following the DNA template activity in the RNA polymerase system of E. coli. Binding to supercoiled and linear pBR322 DNA occurred effectively at 0.05 M NaCl while increasing salt concentrations up to 0.15 M and 0.2 M NaCl caused dissociation of the complexes. Single-stranded DNA showed a slightly lower affinity for the ASBIII protein. ASBIII blocked the DNA template activity of the RNA polymerase reaction in vitro. The binding properties and role of ASB-proteins are discussed with respect to their possible influence on the chromosomal state of the DNA.
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