标题：A robust inducible-repressible promoter greatly facilitates gene knockouts, conditional expression, and overexpression of homologous and heterologous genes in Tetrahymena thermophila
期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2002
卷号：99
期号：6
页码：3734-3739
DOI：10.1073/pnas.052016199
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：The Cd2+-inducible metallothionein (MTT1) gene was cloned from Tetrahymena thermophila. Northern blot analysis showed that MTT1 mRNA is not detectable in the absence of Cd2+, is induced within 10 min of its addition, is expressed in proportion to its concentration, and rapidly disappears upon its withdrawal. Similarly, when the neo1 gene coding region flanked by the MTT1 gene noncoding sequences was used to disrupt the MTT1 locus, no transformants were observed in the absence of Cd2+, and the number of transformants was proportional to increased Cd2+ concentration. The neo3 cassette, in which the MTT1 promoter replaced the histone gene HHF1 promoter of the previously used neo2 cassette, transformed cells at much higher frequencies than neo2 and produced germ-line knockouts where neo2 had failed. Rescuing the progeny of a mating of {gamma}-tubulin gene, GTU1, knockout heterokaryons with a GTU1 gene inserted into the MTT1 locus yielded >75 times more transformants than rescuing with the wild-type GTU1 gene itself. When cells rescued with the MTT1-GTU1 chimeric gene were transferred to medium lacking Cd2+, they stopped growing and had phenotypic changes indistinguishable from cells containing only disrupted GTU1 genes. Thus, it is now possible to create conditional lethal mutants and study the terminal phenotypes of null mutations for essential genes by replacing the endogenous gene with one under the control of the MTT1 promoter. The MTT1 promoter also resulted in {approx}30 times more overexpression of the IAG48[G1] surface antigen gene of the ciliate fish parasite Ichthyophthirius multifiliis than the highly expressed BTU1 promoter, accounting for {approx}1% of the total cell protein. Thus, the MTT1 promoter should enable routine over-expression of endogenous and foreign genes in Tetrahymena.
