Gilley D, Rudman B M, Preer J R, Polisky B
Department of Biology, Indiana University, Bloomington 47405.
Mol Cell Biol. 1990 Apr;10(4):1538-44. doi: 10.1128/mcb.10.4.1538-1544.1990.
A family of genes is responsible for production of surface antigenic components of Paramecium tetraurelia. These surface proteins are expressed in a mutually exclusive manner. Individuals rarely display more than one type. However, changes in environmental conditions can cause different surface proteins which replace preexisting types to be expressed. We investigated the nature of regulation of the genes for the A, C, and H surface antigens of P. tetraurelia. A system for in vitro run-on transcription was developed from crude Paramecium extracts and used in this analysis. The genes for surface antigens A and H were controlled at the level of transcription. However, the gene for surface antigen C demonstrated both transcriptional and posttranscriptional control, depending on the serotype being expressed. When animals expressed serotype A, the gene for surface antigen C was not transcribed. However, when animals expressed serotype H, the gene for surface antigen C was actively transcribed and stable surface antigen C mRNA was present in the cells, although surface antigen C was not detectable by serotype testing or by a salt-alcohol extraction method. The kinetics of transformation from serotype H to serotype C were determined by using the in vitro transcription system and monitoring steady-state RNA levels. During the transition, serotype A transcription was detected in run-on transcription experiments, although this RNA did not accumulate. The results indicate that serotype expression is controlled at several levels and that not all serotype genes are controlled in the same manner.
一个基因家族负责草履虫表面抗原成分的产生。这些表面蛋白以互斥的方式表达。个体很少表现出一种以上的类型。然而，环境条件的变化会导致不同的表面蛋白表达，取代先前存在的类型。我们研究了草履虫A、C和H表面抗原基因的调控性质。从草履虫粗提物中开发了一种体外连续转录系统，并用于该分析。表面抗原A和H的基因在转录水平受到调控。然而，表面抗原C的基因表现出转录和转录后调控，这取决于所表达的血清型。当动物表达血清型A时，表面抗原C的基因不转录。然而，当动物表达血清型H时，表面抗原C的基因被积极转录，细胞中存在稳定的表面抗原C mRNA，尽管通过血清型检测或盐-醇提取法无法检测到表面抗原C。通过使用体外转录系统并监测稳态RNA水平，确定了从血清型H到血清型C的转化动力学。在转变过程中，在连续转录实验中检测到血清型A转录，尽管这种RNA没有积累。结果表明血清型表达在多个水平上受到调控，并非所有血清型基因都以相同的方式受到调控。
