Crystals of the C-terminal domain of the adenovirus single-stranded DNA binding protein (DBP) in complex with the single-stranded oligonucleotide (dT)(16) have been obtained by a batch method from material obtained by chymotryptic digest of full-length DBP. The colorless crystals grow as hexagonal prisms to a maximal size of approximately 0.85 x 0.55 x 0.55 mm. The spacegroup is P3(1)21 with unit cell constants a = 151.5 Angstrom and c = 124.0 Angstrom. There are either three or four molecules of DBP per asymmetrical unit. To improve the reproducibility of crystallization, recombinant protein has been produced using a baculovirus expression system and shown to crystallize under the same conditions. (C) 1995 Academic Press, Inc.