0022-538X/78/0025-0719$02.00/0 Copyright 0 1978 American Society for Microbiology
Printed in U.S.A.
Polyoma Virus-Specific RNA Synthesis in an Inducible Line of Polyoma Virus-Transformed Rat Cells HAIM MANOR* AND ROBERT KAMEN2 Department of Biology and Joseph and Arlene Taub Institute ofBiological Research, Technion-Israel Institute of Technology, Haifa, Israel,' and Imperial Cancer Research Fund, Lincoln's Inn Fields, London WC2A 3PX, England2 Received for publication 7 April 1977
Viral RNA present in the inducible LPT clone 1A of polyoma virus-transformed rat cells was characterized before and after mitomycin C induction by hybridization with 3P-labeled separated E and L strands of polyoma viral DNA restriction endonuclease fragments. In clone 1A celLs maintained under normal growth conditions, the cytoplasm contained a transcript of the E-strand DNA from the "early" region smilar to that previously identified in lytically infected cells, as well as minor quantities of RNA complementary to less than one-half of the Land the E-strand DNA from the "late" region. Nuclei of normally growing cells contained the same species found in the cytoplasm, as well as an additional abundant RNA complementary to one-half of the L-strand DNA of the late region. No significant changes occurred in the cytoplmnic viral RNA after mitomycin C treatment before the onset of viral DNA replication, but the concentration of the nuclear L-strand DNA transcript diminished. After the onset of viral DNA replication after mitomycin C treatment, transcripts of virtually the entire L-strand DNA were found in the nuclei, and a 10-fold increase was observed in the abundance of RNA transcribed from the E strand of the early region. In the cyotplasm, the abundance of the early RNA increased about 25-fold, and late RNA complementary to the L-strand DNA of the late region was found in a similar quantity. The synthesis of both the early and the late RNA species was inhibited if viral DNA replication was blocked with 5-fluorodeoxyuridine. We conclude that the induction of viral DNA replication in LPT cells is not determined at the level of mRNA synthesis. The LPT line of polyoma virus (Py)-transformed rat cells (6) is unusual among Py-transformed cell lines. A relatively high proportion of the LPT cells (0.01 to 0.2%) spontaneously produce infectious virus. Moreover, the proportion of virus-producing cells can be increased to approximately 50% by treatment with various physical and chemical agents (5-7). The average yield of Py DNA in normally growing LPT cultures is 30 to 40 genome equivalents per cell. Only about 20% of this viral DNA remains associated with the chromosomal DNA after alkaline glycerol gradient centrifugation (17); most of the DNA presumably exists in a nonintegrated form (21). The viral DNA in LPT cultures is unequally distributed among the cells. A small proportion of the cells (