Biomedical subjects

X W Deng

Publications and source records attributed to X W Deng.

75 records · Page 5Linked to original sources

PubMed1987

Plastid run-on transcription. Application to determine the transcriptional regulation of spinach plastid genes.

We have developed a spinach plastid run-on transcription system to determine the extent of transcriptional regulation of chloroplast genes during morphogenetic changes of the organelle. In contrast to transcription in a spinach chloroplast extract, which requires initiation of exogenously added genes (Gruissem, W., Greenberg, B. M., Zurawski, G., and Hallick, R. B. (1983) Cell 35, 815-828), RNA synthesis in the run-on system is not affected by heparin or different salt concentrations. Transcription is asymmetric, and the size of the run-on transcripts varies between 75 nucleotides and 8 kilobases. Quantitative filter hybridization studies included gene-specific probes for the ribosomal RNA genes and nine protein-coding genes. Based on the amounts of hybridizable run-on transcripts, these genes can be ordered according to their respective transcriptional activities. The relative transcriptional activities of psbA, rbcL, and atpB in the run-on assay correlate closely with their reported promoter strengths in vitro. The plastid run-on transcription assay has been applied to determine the transcriptional regulation of plastid genes. Hybridization of run-on transcripts to regions of the spinach chloroplast genome containing at least nine tRNA genes indicates that most or all loci are highly transcribed. No significant qualitative and quantitative differences are detected when run-on transcripts from plastids of etiolated and greening cotyledons are hybridized to total, restriction enzyme-digested chloroplast DNA, demonstrating limited transcriptional regulation during chloroplast development.

Chloroplasts↗

PubMed1987

Control of plastid gene expression during development: the limited role of transcriptional regulation.

We have analyzed the transcriptional regulation of plastid genes during chloroplast development in illuminated spinach cotyledons and during leaf formation. The RNAs encoded by plastid genes accumulate with different kinetics during the developmental transitions. Using a novel plastid run-on transcription assay we demonstrate that the transcriptional regulation of a large, diverse group of chloroplast genes is of relatively minor importance for the control of their expression. The general transcriptional activity of the plastid genome increases after illumination and decreases during leaf development. This modulation of general transcriptional activity affects most plastid genes simultaneously and is not correlated with adjustments of the plastid DNA copy number. There are no major changes in the relative transcriptional activities of different genes, although their steady-state mRNA levels change dramatically. The analysis of ten specific plastid genes shows that their relative transcriptional activities are largely maintained throughout the developmental program. This limited transcriptional regulation suggests that plastid gene expression in higher plants is effectively controlled at the posttranscriptional level.

Chloroplasts↗

PubMedDate not supplied

The COP9 complex is conserved between plants and mammals and is related to the 26S proteasome regulatory complex.

The COP9 complex, genetically identified in Arabidopsis as a repressor of photomorphogenesis, is composed of multiple subunits including COP9, FUS6 (also known as COP11) and the Arabidopsis JAB1 homolog 1 (AJH1) ([1-3]; unpublished observations). We have previously demonstrated the existence of the mammalian counterpart of the COP9 complex and purified the complex by conventional biochemical and immunoaffinity procedures [4]. Here, we report the molecular identities of all eight subunits of the mammalian COP9 complex. We show that the COP9 complex is highly conserved between mammals and higher plants, and probably among most multicellular eukaryotes. It is not present in the single-cell eukaryote Saccharomyces cerevisiae, however. All of the subunits of the COP9 complex contain structural features that are also present in the components of the proteasome regulatory complex and the translation initiation factor eIF3 complex. Six subunits of the COP9 complex have overall similarity with six distinct non-ATPase regulatory subunits of the 26S proteasome, suggesting that the COP9 complex and the proteasome regulatory complex are closely related in their evolutionary origin. Subunits of the COP9 complex include regulators of the Jun N-terminal kinase (JNK) and c-Jun, a nuclear hormone receptor binding protein and a cell-cycle regulator. This suggests that the COP9 complex is an important cellular regulator modulating multiple signaling pathways.

Adenosine Triphosphatases↗