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Biomedical subjects

G Link

Publications and source records attributed to G Link.

125 records · Page 7Linked to original sources
PubMed1978

Differential expression of the gene for the large subunit of ribulose bisphosphate carboxylase in maize leaf cell types.

Mesophyll cells and bundle sheath cells, the dimorphic photosynthetic cell types in the C4 plant Zea mays, differ in protein composition. In particular, the large subunit of the chloroplast enzyme ribulose-1,5-bisphosphate carbocylase (EC 4.1.1.39) is found entirely or almost exclusively in bundle sheath cells. The DNA sequence coding for this polypeptide is contained in the chloroplast DNA of both mesophyll cells and bundle sheath cells. RNA complementary to this coding sequence has been detected in RNA from bundle sheath cells, but is almost or entirely absent from mesophyll cells. Similarly, translatable mRNA for this polypeptide has been detected in RNA from bundle sheath cells, but not from mesophyll cells. Portions of the 4200 base pair maize plastid DNA sequence Bam 9 outside the large subunit gene region appear to be transcribed in mesophyll cells. Thus differential gene expression at the mRNA level has been directly demonstrated to occur in these two cell types.

Carboxy-Lyases↗
PubMed1978

Maize plastid gene expressed during photoregulated development.

RNAs larger than about 6 S prepared from etioplasts of dark-grown maize seedlings, and from plastids at later stages of light-induced development, were labeled in vitro and hybridized to separated fragments of maize chloroplast DNA digested with endonucleases. The major nonribosomal RNA present in developing plastids, but virtually undetectable in etioplasts, hybridizes to chloroplast DNA Bam fragment 8 and has been mapped on the maize plastid chromosome. Other aliquots of RNA from plastids were translated in a rabbit reticulocyte-derived system. Developing plastids, and mature chloroplasts, but not etioplasts, contain mRNA for an approximately 34,500 dalton polypeptide. The simultaneous appearance, during light-induced maize plastid development, of RNA which hybridizes to Bam 8 and is translated into a 34,500 dalton protein indicates that photoregulated expression of a single gene is being observed.

Journal Article↗
PubMed1977

Characterization of a protein factor stimulating RNA synthesis by DNA-dependent RNA polymerase II from plant cell cultures.

During purification of DNA-dependent RNA polymerase II (or B) from cell cultures of parsley a protein fraction was separated by phosphocellulose chromatography which enhanced RNA synthesis in the presence of native homologous DNA. This 'stimulatory factor' was characterized in respect to some effects on the reaction catalyzed by RNA polymerase II. In the presence of the factor the metal ion requirements as well as the ionic strength for optimal RNA synthesis were markedly changed; addition of the factor to RNA polymerase II purified by cellulose chromatography restored those enzyme properties which had apparently changed upon this purification step. The chain length of the RNA product synthesized is favouring the view that the factor acts mainly by stabilizing the elongation step during transcription. The stimulatory factor was further purified by several steps of column chromatography. As derived from the results of gel electrophoresis under denaturing conditions the factor consists of several small polypeptides. Those of Mr = 26000, 25000 and 14000 apparently have counterparts among the smaller subunits of highly purified RNA polymerase II from parsley cells. Another polypeptide of the factor, with Mr = 30000, was only found in those preparations of RNA polymerase II which had not been subjected to phosphocellulose chromatography.

DNA-Directed RNA Polymerases↗
PubMed1975

Properties and subunit composition of RNA polymerase II from plant cell cultures.

The purification of DNA-dependent RNA polymerase II (EC 2.7.7.6) from plant cell cultures of Petroselinum (parsley) is described. The procedure during which enzyme I is eliminated includes initial precipitation with (NH4)2SO4, an ultracentrifugation step, gel filtration on Sepharose 4B, chromatography on DEAE-cellulose, DNA-agarose and DEAE-Sephadex. The enzyme purified almost to homogeneity exhibits maximal activity with denatured DNA, and is activated preferentially by Mn2+; alpha-amanitin acts as a strong inhibitor. Electrophoresis of the enzyme in the presence of dodecylsulphate indicates that it is composed of seven subunits with mol. wts of 200 000, 180 000, 140 000, 43 000, 26 000, 25 000 and 16 000. The results of molecular weight and molar ratio determinations suggest that Petroselinum RNA polymerase II may exist in two active forms differing only in the composition of their high molecular weight subunits.

Amanitins↗
PubMedDate not supplied

Structure and expression characteristics of the chloroplast DNA region containing the split gene for tRNA(Gly) (UCC) from mustard (Sinapis alba L.).

The mustard chloroplast gene trnG-UCC is split by a 717-bp group-II intron. Northern hybridization and RNase protection experiments suggest cotranscription with the upstream psbK-psbI operon, but not with the downstream trnR-UCU gene. The ends of most RNase-protected fragments between psbI and trnG correlate with the position of two potential stem-loop structures in this region, which could act as RNA processing elements. However, one RNA 5' end, approximately 75 bp upstream of the trnG 5' exon, does not so correlate and is preceded by prokaryotic-type '-10' and '-35' sequence elements. This suggests the possibility that a fraction of the trnG transcripts is initiated here. All precursor transcripts spanning the trnG region seem to have a common 3' end, which was located 117 bp downstream from the 3' exon, immediately after a stem-loop region. During seedling development, the major 0.8-0.9-kb trnG precursor transcripts show a transient maximum level at around 48 h after sowing, at a time when the mature tRNA begins to accumulate to constant levels. No significant differences in transcript patterns were observed either in the light or in darkness.

Base Sequence↗