In this study, complexes of nucleic acids and acidic nuclear proteins were isolated from baker's yeast cells of Saccharomyces cerevisiae by mild alkaline extraction followed by precipitation with acetic acid. The optimal composition of the buffer applied for extraction of nucleoprotein complexes was determined. The high and low molar mass fractions of the nucleoprotein complexes were separated using cross-flow microfiltration through track-etched membranes. The molar masses were determined by intrinsic viscosity measurements and the molar mass distribution in nucleoprotein complexes was studied by gel permeation chromatography. The protein component of the nucleoprotein complexes was purified on a strongly basic anion exchange resin. The high molar mass nucleoprotein complexes could induce the growth of culture cells of S. cerevisiae exposed to ultraviolet irradiation or treated with hydrogen peroxide. (c) 2006 Elsevier B.V. All rights reserved.