Biomedical subjects

F R Pond

Publications and source records attributed to F R Pond.

5 recordsLinked to original sources

PubMed1994

Characterization of genetic determinants for R body synthesis and assembly in Caedibacter taeniospiralis 47 and 116.

Caedibacter taeniospiralis, an obligate bacterial endosymbiont of Paramecium tetraurelia, confers a killing trait upon its host paramecium. Type 51 R bodies (refractile inclusion bodies) are synthesized by these endosymbionts and are required for expression of the killing trait. The nucleotide sequence of the genetic determinants for type 51 R body synthesis and assembly was determined for C. taeniospiralis 47 and 116. Three independently transcribed genes (rebA, rebB, and rebC) were characterized. To date these are the only genes from C. taeniospiralis to be sequenced and characterized. DNA regulatory regions are recognized by Escherichia coli, and codon usage appears similar to that in E. coli. A fourth open reading frame with appropriate regulatory sequences was found within the reb locus, but no evidence was obtained to suggest that this putative gene is expressed in E. coli. The R body-encoding sequences from both strains are identical. Two-dimensional gel electrophoresis of deletion derivatives shows that two polymerization events are involved in R body assembly. One polymerization event requires only RebB and RebC; the other requires all three proteins. Expression of RebC is necessary for the posttranslational modification of RebA and RebB into species with three and two different molecular weights, respectively. In the presence of RebC, each species of RebB with a different molecular weight has six different isoelectric points.

Amino Acid Sequence↗

PubMed1989

R-body-producing bacteria.

Until 10 years ago, R bodies were known only as diagnostic features by which endosymbionts of paramecia were identified as kappa particles. They were thought to be limited to the cytoplasm of two species in the Paramecium aurelia species complex. Now, R bodies have been found in free-living bacteria and other Paramecium species. The organisms now known to form R bodies include the cytoplasmic kappa endosymbionts of P. biaurelia and P. tetraurelia, the macronuclear kappa endosymbionts of P. caudatum, Pseudomonas avenae (a free-living plant pathogen), Pseudomonas taeniospiralis (a hydrogen-oxidizing soil microorganism), Rhodospirillum centenum (a photosynthetic bacterium), and a soil bacterium, EPS-5028, which is probably a pseudomonad. R bodies themselves fall into five distinct groups, distinguished by size, the morphology of the R-body ribbons, and the unrolling behavior of wound R bodies. In recent years, the inherent difficulties in studying the organization and assembly of R bodies by the obligate endosymbiont kappa, have been alleviated by cloning and expressing genetic determinants for these R bodies (type 51) in Escherichia coli. Type 51 R-body synthesis requires three low-molecular-mass polypeptides. One of these is modified posttranslationally, giving rise to 12 polypeptide species, which are the major structural subunits of the R body. R bodies are encoded in kappa species by extrachromosomal elements. Type 51 R bodies, produced in Caedibacter taeniospiralis, are encoded by a plasmid, whereas bacteriophage genomes probably control R-body synthesis in other kappa species. However, there is no evidence that either bacteriophages or plasmids are present in P. avenae or P. taeniospiralis. No sequence homology was detected between type 51 R-body-encoding DNA and DNA from any R-body-producing species, except C. varicaedens 1038. The evolutionary relatedness of different types of R bodies remains unknown.

Animals↗

PubMed1988

Characterization of Caedibacter endonucleobionts from the macronucleus of Paramecium caudatum and the identification of a mutant with blocked R-body synthesis.

Cytology, DNA and host-symbiont relationships of x-like endosymbionts from Paramecium caudatum are described. The symbionts (Caedibacter caryophila, sp. nov.) live in the macronuclei of their hosts. They confer the killer trait upon their hosts and appear well adapted to their endonucleobiotic way of life. R bodies (proteinaceous ribbons associated with killing) are produced, but differ significantly from any of the four R-body classes previously described. C. caryophila and their R bodies were isolated. DNA was extracted from purified symbionts and used to demonstrate that one P. caudatum line harbors a natural mutant which is deficient in R-body production. Melting studies indicate a GC content of 34.6%. No sequence homology between the C. caryophila DNA and the coding sequence for type 51 R-body production was observed. C. caryophila is parasitic, causing the death of its hosts in starving cultures.

Animals↗

PubMed1986

Organization and expression of genetic determinants for synthesis and assembly of type 51 R bodies.

Type 51 R bodies are produced by all bacterial endosymbionts (Caedibacter taeniospiralis) of Paramecium tetraurelia that confer the hump-killer trait upon their hosts. Type 51 R-body synthesis by C. taeniospiralis is required for expression of the hump-killer trait. The genetic determinants for type 51 R-body synthesis by C. taeniospiralis 47 have been cloned and expressed in Escherichia coli. In this communication we describe three species of polypeptides required for R-body synthesis and the organization of their genetic determinants. Each polypeptide species is controlled by a separate gene that is expressed as an independent transcriptional unit possessing regulatory signals that are recognized by E. coli. Two polypeptide species of 10 and 18 kilodaltons are required for R-body synthesis but apparently are not structural subunits. The third polypeptide species (13 kilodaltons) is the major structural subunit. R-body assembly involves polymerization reactions that result in high-molecular-mass polypeptide complexes, primarily composed of the 13-kilodalton polypeptide species, that appear to be the result of covalent cross-linking between structural subunits. The results presented here have been suggested to apply to the assembly and structure of all type 51 R bodies, but not necessarily to other R-body types.

Animals↗

PubMed1983

Incorporation of selenium-75 into semen and reproductive tissues of bulls and rams.

After intramuscular injections of 500 muCi 75Se, semen was collected periodically over a 63-day period from a selenium-deficient and a selenium-injected ram which were then killed for collection of the reproductive organs for the gel filtration studies. Testes, accessory glands and semen were also obtained from a bull injected intravenously with 75Se. Gel filtration (Sephadex G 150) of ram testis cytosol resulted in 4 75Se peaks (Ve/Vo ratios of 1 X 1, 1 X 5, 2 X 3, 2 X 9). In the selenium-injected ram the glutathione peroxidase (GSH-Px) peak (Ve/Vo 1 X 5) predominated, but in the selenium-deficient ram, radioactivity of the GSH-Px peak was less than that of the higher molecular weight peak (Ve/Vo 1 X 1). Gel filtration chromatograms of bull testis cytosol yielded 5 75Se peaks (Ve/Vo 1 X 1, 1 X 5, 1 X 9, 2 X 4, 2 X 8). In chromatograms of ram seminal plasma on Sephacryl S-200 there were 2 major (Ve/Vo 1 X 4, 1 X 1) and 2 minor peaks (Ve/Vo 1 X 7, 2 X 4). 75Se increased with time up to 49 days after injection in all peaks. 75Se-labelled bull seminal plasma yielded 2 75Se peaks (Ve/Vo 1 X 1, 1 X 4) which corresponded to the major peaks of ram seminal plasma. Bull and ram seminal plasma GSH-Px activities per mg protein were comparable (28 and 29 nmol NADPHox/min, respectively), but when expressed per ml seminal plasma, activity of the bull was more than 7 times the highest activity of ram seminal plasma (2908 and 385 nmol NADPHox/min, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗