Subunits of yeast RNA polymerase I involved in interactions with DNA and nucleotides

Reaction of yeast RNA polymerase I with pyridoxal 5′-phosphate and sodium borohydride under conditions which inactivate the enzyme results in the specific binding of pyridoxal 5′-phosphate to subunits of 185,000, 137,000, 48,000 and 36,000 daltons. Nucleotides, which protect the enzyme from inactivation specifically inhibit the binding of pyridoxal 5′-phosphate to subunits of 185,000 and 137,000 daltons. DNA which also protects the enzyme from inactivation by pyridoxal 5′-phosphate prevents the binding of the reagent to the four polypeptides. These results suggest that subunits of 185,000 and 137,000 are involved in interactions with both nucleotides and DNA presumably of the type leading to initiation and/or polymerization and that subunits of 48,000 and 36,000 daltons also bind to DNA but this interaction is not strictly required for polymerase activity.