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We report that the 1.5-and 7.5-kilobase-pair (kbp) transposonlike sequences present in the R-body-coding plasmids of Caedibacter taeniospiralis share homology. The R-body-coding plasmids of two new strains of C. taeniospiralis, derived from strains 169 and A30, carry the 7.5-and 1.5-kbp elements, respectively, inserted at new positions. Sequences homologous to the 7.5-kbp sequence from C. taeniospiralis 47 were detected in the chromosomes of three other strains of C. taeniospiralis.All members of the bacterial species Caedibacter taeniospiralis are obligate cytoplasmic endosymbionts of the freshwater ciliate Paramecium tetraurelia. These bacteria, commonly known as hump killer kappa particles, confer the hump killer trait on their protozoan hosts. In addition, C. taeniospiralis is notable in its ability to synthesize a large inclusion body known as an R body. R bodies are long (approximately 10 ,um), proteinaceous ribbons about 0.5 ,um wide and 13 nm thick, which are rolled up inside the bacterial cell, forming hollow cylinders (1). All strains of C. taeniospiralis carry plasmids (2,7,8). The functions of these plasmids are, for the most part, unknown. However, one function (R-body production) has been demonstrated (9), and another (the killer trait) has been suggested (2).Restriction endonuclease analysis has shown that the R-body-coding plasmids of six strains of C. taeniospiralis have very similar physical maps (8). In every case, the differences observed among these plasmids can be accounted for by single insertion events involving DNA sequences that are about 1.5 or 7.5 kilobase pairs (kbp) in length. In this communication, we report that these inserted sequences share homology with each other and that they appear to be transposable genetic elements.The strains of C. taeniospiralis used in this study are listed in Table 1. Plasmid DNA was purified from these strains with ethidium bromide-cesium chloride gradients as previously described (10). Both upper and lower bands were collected from gradients. Conditions for restriction endonuclease digestions and agarose gel electrophoresis were as previously described (10). Agarose gels were stained for approximately 5 min in ethidium bromide (10 jig/ml) and photographed. To obtain Southern blots (14) of agarose gels, we denatured restriction endonuclease-generated DNA fragments in situ and then transferred them to Gene Screen membranes (New England Nuclear Corp., Boston, Mass.) per the manufacturer's instructions. The recombinant plasmid pBQ54 (9) was used as a probe in Southern blot hybridizations. Probe DNA was radiolabeled by nick translation with 32P-dCTP (ICN Pharmaceuticals, Inc., Irvine, Calif.) as previously described (6 radiolabeled pBQ54 were carried out at 60°C by the method described by Maniatis et al. (5). Physical maps of pKAP30-1 and pKAP169-1 were determined by restriction endonuclease analysis as previously described (10), in which DNA fragment profiles generated by single and double restriction endonuclease digestions were compared. Restriction en...

The relationship of type 51 refractile (R) bodies to R bodies produced by Pseudomonas taeniospiralis was investigated. Proteins associated with type 51 R bodies were not serologically cross-reactive with proteins associated with R bodies from P. taeniospiralis. The genetic determinants for type 51 R bodies did not exhibit close homology with DNA sequences from P. toeniospiralis.Refractile (R) bodies are inclusion bodies known to occur in only two genera of bacteria, Caedibacter and Pseudomonas. They are proteinaceous ribbons that, in their natural state, are rolled up, forming hollow cylinders resembling rolls of dialysis tubing. Until recently, all known species of R-body-producing bacteria were assigned to the genus Caedibacter (7-9). These bacteria, commonly known as kappa particles, are obligate endosymbionts of paramecia and confer killer traits upon their hosts. However, two free-living soil microorganisms, Pseudomonas taeniospiralis and Pseudomonas avenae, are now known to possess the ability to produce R-body-like structures (2,4,15). R bodies can be grouped into the following four basic types.(i) Type 51 R bodies are produced by Caedibacter taeniospiralis. These bacteria confer the hump killer trait on their hosts (Paramecium tetraurelia). Synthesis of type 51 R bodies is required for expression of the hump killer trait by host paramecia (la, lb, 16). Inside the bacterial cell, these R bodies are up to 0.5 I.m wide and 0.5 ,um in diameter. Both termini of a type 51 R-body ribbon form acute angles. When unrolled, the R-body ribbon attains lengths of up to 15 ,um (1). When exposed to a pH of less than 6.5, type 51 R bodies unroll from the inside in a telescoping fashion. This process can be reversed by returning the pH to neutrality. The genetic determinants of type 51 R bodies are plasmid borne and have been cloned and expressed in Escherichia coli (11).(ii) Type 7 R bodies are produced by all other species of Caedibacter. These bacteria also confer killer traits (though not the hump killer trait) upon host paramecia. The (iii) R bodies produced by P. taeniospiralis are smaller than those produced by other R-body-producing bacteria. They are generally about 0.2 ,um in length and 0.25 ,um in diameter and resemble type 51 R bodies in that they unroll from the inside (3). However, unrolling is not pH dependent and is irreversible, as with type 7 R bodies. They further resemble type 7 R bodies in that their outer termini are blunt and their inner termini form acute angles (3).(iv) R bodies produced by P. avenae are morphologically distinct from the other three types (15). The unrolled ribbon does not exhibit any parallel edges. The unrolled ribbon is widest at the midpoint and narrows progressively toward the termini where very acute (approximately 150) angles are formed. These R bodies unroll in response to decreasing pH; however, in contrast to type 51 R bodies, they are reported to do so from the outside (6). In the rolled form, these R bodies are larger than the other types (0.5 to 0.8 p.m long by 0.5 ...

C4 and Slp are highly homologous mouse genes that differ in function and regulation. Allelic variants exist in quantitative regulation of C4 and in hormonal regulation of Slp. We have examined expression in several tissues, including liver and peritoneal macrophages which are the major sites of synthesis, using a probe that allows direct comparison of C4 and Slp mRNAs. Correctly-sized and initiated RNA, within an order of magnitude of liver levels, is found in mammary gland, lung, spleen, and kidney; lower levels are detectable in testis, brain, heart and submaxillary gland. By comparing expression in congenic mouse strains differing in C4 and Slp loci, regulation of these genes is seen to vary in different tissues. This provides a well-defined genetic system in which to examine cis-acting sequences and trans-acting factors that result in tissue-specific patterns of gene regulation.