Paramecium tetraurelia can be transformed by microinjection of cloned serotype A gene sequences into the macronucleus. Transformants are detected by their ability to express serotype A surface antigen from the injected templates. After injection, the DNA is converted from a supercoiled form to a linear form by cleavage at nonrandom sites. The linear form appears to replicate autonomously as a unit-length molecule and is present in transformants at high copy number. The injected DNA is further processed by the addition of parameciumtype telomeric sequences to the termini of the linear DNA. To examine the fate of injected linear DNA molecules, plasmid pSA14SB DNA containing the A gene was cleaved into two linear pieces, a 14-kilobase (kb) piece containing the A gene and flanking sequences and a 2.2-kb piece consisting of the procaryotic vector. In transformants expressing the A gene, we observed that two linear DNA species were present which correspond to the two species injected. Both species had Paramecium telomerelike sequences added to their termini. For the 2.2-kb DNA, we show that the site of addition of the telomerelike sequences is directly at one terminus and within one nucleotide of the other terminus. These results indicate that injected procaryotic DNA is capable of autonomous replication in Paramecium macronuclei and that telomeric addition in the macronucleus does not require specific recognition sequences.Foreign DNA introduced into eucaryotic cells can suffer a variety of fates depending on the sequences introduced and the system used. In mouse L cells in culture, injection of multiple copies of either supercoiled or linear DNA molecules into nuclei can result in integration into host chromosomes at a limited number of sites of head-to-tail concatamers of the input DNA (7, 18). These concatamers result from highly efficient homologous recombination mediated by host recombinational machinery. Alternatively, microinjection of a variety of different supercoiled DNA species into unfertilized Xenopus laevis eggs leads to autonomous replication of the injected DNA as supercoiled forms, apparently regardless of sequence (13,16). In the yeast Saccharomyces cerevisiae, foreign supercoiled DNA introduced by transformation replicates autonomously only if it contains distinctive sequences called autonomously replicating sequences (21), presumably reflecting specific recognition of certain sequences by host replication machinery.We describe here another fate for DNA introduced into the ciliated protozoan Paramecium tetraurelia. We have previously described a transformation system in which exogenous DNA is introduced into the macronuclei of recipients by microinjection (10). Our assay for transformation involves the synthesis of specific cell surface antigens called immobilization antigens (for a review, see reference 19). Paramecia can alter their surface antigens under different environmental conditions. In general, they express only one type at a time. Eleven different serotypes have been described for stock ...

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Epigenetic inheritance includes all non-Mendelian inheritance, in fact any inheritance that does not arise from base changes. Ciliates, particularly Paramecium and Tetrahymena, undergo epigenetic changes to their macronuclei when they are formed at nuclear reorganization. Once set, however, they are reproduced in a constant fashion, except for allelic segregations, during vegetative fissions in Tetrahymena and certain life cycle changes in both Paramecium and Tetrahymena. This review is meant to be inclusive, discussing all the known cases of epigenetic changes in macronuclei. They involve virtually all traits. We find that these macronuclear changes are subject to a variety of modifications in the way that they are implemented. They constitute a major feature of ciliate genetics, probably because the separation of generative and vegetative functions to micronuclei and macronuclei makes such changes possible.

Kappas (bacterial symbionts containing R bodies) have been studied in 16 strains of Paramecium aurelia, syngens 2 and 4. All produce toxins capable of killing sensitive paramecia. The first major class, the 51 group (consisting of the kappas of strains 51, 116, and 298), has R bodies which, when the pH is lowered below 6.5, unwind reversibly from the inside to form a tight tube; the outside end of the R-body ribbon forms an acute angle; no sheath surrounds the R body. The phage-like structures of the 51 group are helical; no capsomere-like structures are present; isolated R bodies do not have any killing activity. The second major class, the 7 group (strains 7, 576, Bl 166-1, 249, 1041, 310, 1039), has R bodies which unwind irreversibly from the outside to form a loose twisted ribbon whose outside tip is blunt, irregular or finger-like; a single membraneous sheath covers the R body. Phage-like structures in the 7 group are spherical; capsomere-like structures are present; isolated R bodies show killing activity. The third major class, the 562 group (strains 562, 517, 511), is similar to the 7 group except that there is no sheath, no capsomeres, and free R bodies are almost or completely inactive. The phage-like structures are spherical, and unlike those of the 7 group, do not stick to the R bodies. In addition to these 3 major classes there are 3 strains which show important differences from the major classes and also differ among themselves. 1038 is like 7 in all respects except that the phage-like structures are helical and isolated R bodies are not very active. 51ml, presumably a mutant of 51, has spherical phage-like structures and 7 type-R bodies which are inactive when isolated. 570 is the only known mate-killer with R bodies; it has spherical phage-like structures. It is noted that strain 1039 of the 7 group has very few phage-like structures, virtually all of which are empty. Since free 1039 R bodies are highly active, it is likely that intact phage-like structures are not essential for the toxic action on sensitives. The spherical and helical phage-like structures are probably very closely related because 51, which has helical structures, apparently gave rise to 51m1, which has spherical structures. Likewise the kappa symbionts of 1038 with helical phage-like structures are virtually identical to the kappas of the 7 group with spherical phage-like structures. The presence of phage-like structures in all strains with R bodies suggests that R bodies may be a product of phage activity. Strain 570, a mate-killer whose symbionts contain R bodies, provides a link between kappas and mus, the mate-killer symbionts. The symbionts of 570 are the only ones containing R bodies which are non-toxic when encountered by sensitives in the medium in which the paramecia are cultured.