Purified simian virus 40 and polyoma DNAs injected into nuclei of Xenopus Nuclei from various eukaryotic cells injected into frog oocyte nuclei (germinal vesicles) continue to direct synthesis of origin-specific proteins (1). In addition, genes that were not expressed in the donor cell may be activated after injection (2). Purified viral, phage, or plasmid DNAs injected into the nucleus of Xenopus oocytes serve as templates for the transcription of specific RNA sequences (3). The synthesis of 5S RNA (4) and tRNA (5) is greatly stimulated upon injection of the corresponding templates. It has been claimed that, after injection of simian virus 40 (SV40) DNA I (6), much of the virus-specific RNA synthesized in the Xenopus oocyte has the same size and is transcribed from the same region as the late viral mRNAs present in lytically infected monkey cells (7,8), and proteins that migrate on two-dimensional gels in the same manner as the SV40 capsid proteins VP 1 and VP 3 were detected (8).In this article we report that Xenopus oocytes transcribe and translate most or all of the genetic information contained in the SV40 genome. In particular, we observed the synthesis of large (T) and small (t) SV40 tumor antigens having the same characteristics as those synthesized in monkey cells undergoing lytic infection. Injection of polyoma DNA I (6) resulted in the synthesis of three polyoma-specific polypeptides comigrating, during gel electrophoresis, with two minor polypeptides related to polyoma tumor antigen and with the major capsid protein, respectively.MATERIALS AND METHODS SV40 DNA I (covalently closed circular) was isolated from SV40-infected CV-1 African green monkey cells (Flow Laboratories, Irvine, Scotland) 40-48 hr after infection by selective extraction, deproteinized with phenol, and purified by CsCl/ethidium bromide density gradient equilibrium centrifugation (9). Polyoma DNA I was isolated from polyomainfected mouse kidney cell cultures 30-35 hr after infection by the same procedure. For injection, the viral DNA was dissolved in 88 mM NaCl/1 mM KCI/15 mM Tris-HCl, pH 7.6 at concentrations between 300 and 500 Ag/ml. 24 hr in Barth's solution containing 50 units per ml each of streptomycin, penicillin, and kanamycin. Thereafter 1 ml of Barth's solution containing 300 ,uCi of [35S]methionine (500-1000 Ci/mmol, the Radiochemical Centre, Amersham, England) was added and incubation was continued for another 24 hr (1 Ci = 3.7 X 1010 becquerels). The surviving oocytes (60-90%) were washed first with Barth's solution, then with distilled water, and stored at -80'C after removal of the water.For extraction of viral proteins, the oocytes were disrupted in a small Dounce homogenizer in 2 ml of a buffer containing detergent (0.1 M Tris-HCl, pH 9/0.1 M NaCl/5 mM KCI/1 mM CaCl2/0.5 mM MgCl2/0.7 mM Na2HPO4/0.5% Nonidet P-40). The homogenate was sonicated in a MSE ultrasonic disintegrator (Mk 1) for 1 min with an amplitude of 10 Atm and kept on ice for 20 min. After centrifugation at 15,000 X g for 30 min at 40C the s...