Biomedical subjects

J T Beatty

Publications and source records attributed to J T Beatty.

44 records · Page 3Linked to original sources

PubMed1989

Structural and functional analysis of transcriptional control of the Rhodobacter capsulatus puf operon.

We report data indicating that the Rhodobacter capsulatus puf operon promoter and the site for its oxygen regulation are located more than 700 base pairs upstream from the previously identified puf genes and have identified the nucleotide sequences that constitute these control signals. A model is proposed in which a polycistronic transcript at least 3.4 kilobases in length is initiated near the O2-regulated promoter and is processed posttranscriptionally by endonucleolytic cleavage at multiple sites, yielding discrete mRNA segments that are degraded at different rates. A newly identified gene (pufQ), which includes a hydrophobic domain having some similarity to domains of the products of the pufL and pufM genes, begins 313 nucleotides into the puf transcript and is located entirely within the most rapidly degraded segment of the transcript. A previously identified puf transcript segment encoding structural proteins for photosynthetic membrane complexes persists after degradation of the most 5' region of the transcript and is itself subject to segmentally specific degradation. Our results suggest a model in which differential expression of the multiple genes encoded by the puf operon is at least in part attributable to major differences in the rates of decay of the various segments of puf mRNA.

Amino Acid Sequence↗

PubMed1988

An intercistronic stem-loop structure functions as an mRNA decay terminator necessary but insufficient for puf mRNA stability.

Segmental differences in stability within the polycistronic transcripts of the puf operon contribute to differential expression of photosynthesis genes in R. capsulatus. The comparatively stable 5' segment of these transcripts ends in a large intercistronic stem-loop structure. We show here that deletion of this RNA hairpin destabilizes the 5' puf mRNA segment but that its insertion at the 3' end of the puf operon transcripts fails to stabilize the labile 3' puf mRNA segment. Evidence is presented that decay of the 3' segment begins with endonucleolytic cleavage in which the intercistronic stem-loop structure does not participate. We conclude that this RNA hairpin is necessary but insufficient for the stability of mRNA upstream of it, and that it functions in message degradation solely as an mRNA decay terminator that protects upstream mRNA segments from degradation by 3' exoribonucleases.

Bacterial Proteins↗

PubMed1988

Posttranscriptional regulation by light of the steady-state levels of mature B800-850 light-harvesting complexes in Rhodobacter capsulatus.

Photosynthetic organisms exhibit a variety of responses to changes in light intensity, including differential biosynthesis of chlorophyll-protein complexes. Cultures of Rhodobacter capsulatus grown anaerobically with a low intensity of light (2 W/m2) contained about four times as much B800-850 light-harvesting complex as cells grown under high light intensity (140 W/m2). The mRNA transcripts encoding B800-850 beta and alpha peptides were analyzed by Northern blot (RNA blot), S1 nuclease protection, and capping with guanylyl transferase. It was found that the steady-state levels of B800-850 mRNAs in high-light-grown cultures were about four times as great as in cells grown under low light intensity. Therefore, the lesser amounts of mature B800-850 peptide gene products found in cells grown with high light intensity are the result of a posttranscriptional regulatory process. It was also found that there are two polycistronic messages encoding the B800-850 peptides. These messages share a common 3' terminus but differ in their 5'-end segments as a result of transcription initiation at two discrete sites. Moreover, the half-lives of B800-850 mRNAs were about 10 min in cells grown with high light and approximately 19 min in cultures grown with low light. It is concluded that there must be more frequent initiations of transcription of B800-850 genes in cells grown with high light than in those grown with low light, and that the relative amounts of B800-850 complexes under these conditions are controlled by a translational or posttranslational mechanism.

Bacterial Proteins↗

PubMed1986

Expression of cellulase genes in Rhodobacter capsulatus by use of plasmid expression vectors.

Broad-host-range plasmid vectors were constructed for expression of heterologous genes in the photosynthetic bacterium Rhodobacter capsulatus. These plasmids utilize an RK2-derived replicon for maintenance and conjugative transfer and the R. capsulatus rxcA promoter to obtain transcription of genes within appropriately positioned DNA fragments. The expression vectors were used to obtain synthesis of endoglucanase and exoglucanase in R. capsulatus from cellulase genes present on exogenously derived DNA fragments. The cellulase genes were expressed either by use of their native translation initiation signals or by in-frame fusion with the rxcA B870 beta gene translation initiation signals to form a hybrid protein. The level of cellulase gene expression was found to be modulated in response to the extent of aeration of plasmid host cultures.

Cellulase↗

PubMed1985

Differential expression of photosynthesis genes in R. capsulata results from segmental differences in stability within the polycistronic rxcA transcript.

We report that the light-harvesting and reaction center genes in the rxcA locus of R. capsulata are contained within a single operon and that their differential expression results predominantly from marked segmental differences in stability within the polycistronic rxcA transcript. The 3' portion of this transcript is rapidly degraded to give rise to either of two slowly decaying mRNA remnants, both of which encode only the light-harvesting polypeptides. The greater stability of these remnants accounts for nearly all of the difference between the concentrations of the light-harvesting and reaction center proteins. The unstable 3' portion of the transcript is delimited by two alternative stem-and-loop structures, which apparently act as barriers to 3' exoribonucleases and thereby protect the upstream RNA segment. When a DNA fragment containing the rxcA locus was fused to a plasmid promoter and transcribed in E. coli, the long precursor transcript was processed to two short messages of greater stability, as in R. capsulata.

Bacterial Proteins↗

PubMed1983

Hybridization of cloned Rhodopseudomonas capsulata photosynthesis genes with DNA from other photosynthetic bacteria.

The homology of Rhodopseudomonas capsulata DNA segments carrying photosynthesis genes with sequences present in total DNA from certain other photosynthetic and non-photosynthetic bacterial species was determined by hybridization. R. capsulata DNA fragments that carry loci for production of peptide components of the photosynthetic reaction center and light-harvesting I antenna complex were found to hybridize to DNA from some photosynthetic species. However, fragments that carry carotenoid or bacteriochlorophyll biosynthesis genes showed either weak or undetectable heterospecific hybridization under the conditions employed.

Bacterial Proteins↗

PubMed1981

Slow potential shifts of human brain during forewarned reaction.

The slow brain potentials observed during the 4 sec interstimulus interval (ISI) of a CNV paradigm were investigated by a factorial manipulation of the parameters that have been identified as affecting the CNV at ISIs of 1 or 2 sec. Subjects performed choice and simple reaction time (RT) tasks under all possible combinations of auditory and visual warning (S1) and imperative (S2) stimuli. The choice task involved easy or difficult intensity discriminations at S2, which were forewarned by S1s that cued the subject as to the level of difficulty for that trial. Principal components analysis (PCA) of the data revealed two negative afterwave factors and a late positive component (LPC) related to warning stimulus variables, and a late negative shift preceding S2 that was related to motor preparation. The negative afterwave components were enhanced in the choice RT task, and the earlier of the two components showed a modality-specific distribution. The LPC factor was also enhanced in the choice task and was further enhanced by S1s signaling difficult discriminations. Additionally, the LPC was larger for visual S1s. The S1-related components are interpreted in terms of orienting, while the later shift is identified with the readiness potential and motor preparation. The results support the notion that the conventionally recorded CNV consists of S1 evoked and response-related potentials rather than non-specific and modality-specific anticipatory potentials.

Action Potentials↗

PubMed1981

Biosynthetic and bioenergetic functions of citric acid cycle reactions in Rhodopseudomonas capsulata.

Rhodopseudomonas capsulata can grow in a number of alternative modes, including (i) photosynthetic, defined here as anaerobic growth with light as the energy source, and (ii) heterotrophic, referring to aerobic heterotrophic growth in darkness. The functions of citric acid cycle sequences in these growth modes were investigated using wild-type and appropriate mutant strains. Results of growth tests and O(2) utilization experiments showed that in the heterotrophic mode, energy conversion is dependent on operation of the classical citric acid cycle. Alpha-ketoglutarate dehydrogenase (KGD) activity in wild-type strain B10 is substantially higher in cells grown heterotrophically than in cells grown photosynthetically. Molecular oxygen, even at low concentration, appears to be important in regulation of KGD synthesis and, thus, in expression of citric acid cycle activity. Extracts of (photosynthetically grown) mutant strain KGD11 lack demonstrable KGD activity, and in contrast to the wild type, KGD11 is unable to grow heterotrophically on succinate, malate, or pyruvate owing to failure of the energy conversion function of the citric acid cycle. KGD11, however, grows well photosynthetically on malate or on CO(2) + H(2). The KGD activity level required to support the bioenergetic function of the citric acid cycle is evidently much higher than that necessary to satisfy biosynthetic demands; thus, a very low rate of succinyl-coenzyme A formation (needed for biosynthesis) in the mutant would suffice for growth under photosynthetic conditions. In wild-type R. capsulata, the alpha-ketoglutarate required for glutamate synthesis is ordinarily generated via citric acid cycle reactions, which include the conversions catalyzed by citrate synthase and isocitrate dehydrogenase. Mutants blocked in the former or both of these enzymes can grow photosynthetically if provided with an exogenous source of alpha-ketoglutarate or glutamate, but grow very poorly (if at all) as heterotrophs since the energy supply under these conditions depends on operation of the complete citric acid cycle.

Citrate (si)-Synthase↗