ADENOVIRUS (AD) AND SV40---MOLECULAR AND CELLULAR BIOLOGY

染色体突变是大多数遗传病的根本原因。 遗传性疾病和许多发育异常。 突变也可以导致基因表达的改变， 体细胞，导致正常分化的细胞丧失， 表型并最终转化为细胞。 我们 研究突变的机制，使用基于SV 40的 穿梭载体作为探针研究分子机制 通过这种方式，损伤DNA的物质会诱导 哺乳动物细胞 通过使用穿梭载体， 广泛表征了发生在 哺乳动物细胞自发或响应DNA 损害 分析这些突变的序列特异性 这一模型解释了哺乳动物的DNA 聚合酶在DNA合成过程中引入错误， 突变。 载体在体外DNA复制中的研究 系统表明，除了DNA之外， 聚合酶，似乎影响复制保真度。 进一步 使用该系统的研究应允许表征这些 生物化学水平的因素。 了解细胞调节的机制 增殖和分化是理解 多细胞生物的发展。 的一种方法 研究这些调节机制是为了研究 转化细胞的行为。 在过去的几年里，我们 一直在研究促有丝分裂和抗有丝分裂生长因子 由Ad 2和SV 40转化的仓鼠细胞分泌。 我们 结果表明，SV 40转化细胞，而不是Ad 2- 转化的细胞，分泌促有丝分裂抑制剂（MI）， 抑制未转化仓鼠细胞的增殖反应 和用血清促分裂剂刺激的正常大鼠细胞。 米还 抑制正常仓鼠脾脏的促有丝分裂反应 用凝集素刺激的淋巴细胞激活T细胞 （伴刀豆球蛋白A）或B细胞（美洲商陆有丝分裂原）。 我们有 提出，MI可能有助于高致癌性的 SV 40转化细胞，通过干扰 免疫效应细胞在肿瘤生长部位。 我们也 利用SV 40研究病毒组织嗜性的遗传基础。 我们 发现皮下注射SV 40的小t抗原突变体， 经常诱发仓鼠腹部淋巴瘤，而不是 野生型SV 40诱导的皮下纤维肉瘤。 的 突变体可能不能产生所需的生长因子， 非增殖细胞的体内转化。

Chromosomal mutations are the underlying cause of most inherited diseases and many developmental abnormalities. Mutations can also lead to alterations in gene expression in somatic cells, leading to loss of the normal differentiated phenotype and ultimately to cellular transformation. We are studying the mechanism of mutagenesis, using an SV40-based shuttle vector as a probe to investigate the molecular mechanisms by which agents that damage DNA induce mutations in mammalian cells. Through use of the shuttle vector, we have extensively characterized the types of mutations that occur in mammalian cells either spontaneously or in response to DNA damage. Analysis of the sequence specificity of these mutations has led to a model which explains how the mammalian DNA polymerase introduces errors during DNA synthesis, causing mutations. Studies with the vector in an in vitro DNA replication system indicate that cellular factors, in addition to DNA polymerase, appear to influence replication fidelity. Further studies with this system should allow a characterization of these factors on the biochemical level. Understanding the mechanisms of regulation of cellular proliferation and differentiation is basic to understanding development of multicellular organisms. One approach to investigating these regulatory mechanisms is to study the behavior of transformed cells. For the past several years, we have been studying mitogenic and antimitogenic growth factors secreted by hamster cells transformed by Ad2 and SV40. Our findings indicate that SV40-transformed cells, but not Ad2- transformed cells, secrete a mitogenic inhibitor (MI) that strongly inhibits a proliferative response in untransformed hamster cells and normal rat cells stimulated with serum mitogens. MI also inhibits a mitogenic response by normal hamster spleen lymphocytes stimulated with lectins that activate T cells (concanavalin A) or B cells (pokeweed mitogen). We have proposed that MI might contribute to the high oncogenicity of the SV40-transformed cells by interfering with mobilization of immune effector cells at the site of tumor growth. We are also using SV40 to study the genetic basis of viral tissue tropism. We find that subcutaneously injected small t-antigen mutants of SV40 often induce abdominal lymphomas in hamsters, rather than the subcutaneous fibrosarcomas induced by wild-type SV40. The mutants may fail to produce a growth factor required for the in vivo transformation of non-proliferating cells.