The role of macronuclear DNA sequences in the permanent rescue of a non-mendelian mutation in Paramecium tetraurelia.
The paramecium tetraurelia mutant called d48 has a complete copy of the A surface protein gene in its micronuclei, but lacks the A gene in the macronucleus. Previous experiments have shown that microinjection of a plasmid containing the entire A gene or a large portion of the gene into the macronucleus of d48 rescued the cell line after formation of a new macronucleus (autogamy). Here we show that several different regions of the A gene can rescue d48, but 100% of the activity cannot be localized to a single, defined region. Inversion of a sequence contained within an A gene plasmid had no measurable effect on rescue efficiency and co-injection of two different plasmids results in enhancement of rescue activity despite the non-contiguous form of the DNA sequences. Both these results suggest that no specific product (RNA or protein) with defined end points is made from the rescuing fragment. A unique restriction site was created in the A gene and used to demonstrate that the injected DNA does not serve as a direct template for the synthesis of the new macronuclear DNA. Models to explain the action of the injected DNA are discussed.
You
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Department of Biochemistry, Purdue University, West Lafayette, Indiana 47907-1153.
Scott
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Forney
J
J
D000818:Animals; D000953:Antigens, Protozoan; D000954:Antigens, Surface / Q000235:genetics; D002467:Cell Nucleus / Q000378:metabolism; D016054:DNA, Protozoan; D005821:Genetic Techniques; D009154:Mutation; D010247:Paramecium / Q000235:genetics*; D015800:Protozoan Proteins / Q000235:genetics; D012680:Sensitivity and Specificity; D013698:Templates, Genetic
D000953:Antigens, Protozoan; D000954:Antigens, Surface; D016054:DNA, Protozoan; D015800:Protozoan Proteins; C043323:immobilization antigens