Biomedical subjects

G K Lamppa

Publications and source records attributed to G K Lamppa.

22 records · Page 2Linked to original sources

PubMed1987

Processing of a wheat light-harvesting chlorophyll a/b protein precursor by a soluble enzyme from higher plant chloroplasts.

A processing activity has been identified in higher plant chloroplasts that cleaves the precursor of the light-harvesting chlorophyll a/b-binding protein (LHCP). A wheat LHCP gene previously characterized (Lamppa, G.K., G. Morelli, and N.-H. Chua, 1985. Mol. Cell Biol. 5:1370-1378) was used to synthesize RNA and subsequently the labeled precursor polypeptide in vitro. Incubation of the LHCP precursors with a soluble extract from lysed chloroplasts, after removal of the thylakoids and membrane vesicles, resulted in the release of a single 25-kD peptide. In contrast, when the LHCP precursors were used in an import reaction with intact pea or wheat chloroplasts, two forms (25 and 26 kD) of mature LHCP were found. The peptide released by the processing activity in the organelle-free assay comigrated with the lower molecular mass form of mature LHCP produced during import. Properties of the processing activity suggest that it is an endopeptidase. Chloroplasts from both pea and wheat, two divergent higher plants, contain the processing enzyme, suggesting its physiological importance in LHCP assembly into the thylakoids. We discuss the implications of LHCP precursor processing by a soluble enzyme that may be in the stromal compartment.

Amino Acid Sequence↗

PubMed1985

Structure and developmental regulation of a wheat gene encoding the major chlorophyll a/b-binding polypeptide.

A genomic clone for a major chlorophyll a/b-binding polypeptide of the light-harvesting complex has been sequenced from wheat. This gene, whAB1.6, encodes a 70-nucleotide 5'-nontranslated spacer, a 34-amino-acid NH2-terminal extension, i.e., the transit peptide, and a mature coding protein of 232 amino acid residues. The exact molecular weight of the precursor polypeptide is 28,560. The transit peptide is basic and is rich in serines. No intervening sequences are found in this gene. The transcription start site of the whAB1.6 gene occurs at AAAC as determined by S1 nuclease analysis. Putative regulatory sequences occur upstream of the gene at -25 (TTTAAATA) and at -72 (CCAACCA). Northern blots show a single RNA species estimated to be 1,100 nucleotides. Heterogeneity of the RNA population is demonstrated in S1 nuclease analyses with a 5'-end-labeled fragment that extends 191 nucleotides into the mature protein coding sequence. At least seven different transcripts can be recognized. The highest levels of RNA transcribed from the whAB1.6 gene are found in the basal segments of the wheat leaf, whereas other chlorophyll a/b-binding transcripts in the cell show a different pattern of abundance. As a control, we show that roots do not contain chlorophyll a/b-binding RNA. The most abundant RNA species shows an interrupted homology with the whAB1.6 gene at the start of the mature protein coding sequence; another species shows homology beginning at the start of the transit peptide and does not include the nontranslated region. Chlorophyll a/b-binding polypeptides accumulate toward the tip of the leaf as shown by Western blot analysis of total thylakoid proteins.

Amino Acid Sequence↗

PubMed1979

Chloroplast DNA Sequence Homologies among Vascular Plants.

The extent of sequence conservation in the chloroplast genome of higher plants has been investigated. Supercoiled chloroplast DNA, prepared from pea seedlings, was labeled in vitro and used as a probe in reassociation experiments with a high concentration of total DNAs extracted from several angiosperms, gymnosperms, and lower vascular plants. In each case the probe reassociation was accelerated, demonstrating that some chloroplast sequences have been highly conserved throughout the evolution of vascular plants. Only among the flowering plants were distinct levels of cross-reaction with the pea chloroplast probe evident; broad bean and barley exhibited the highest and lowest levels, respectively. With the hydroxylapatite assay these levels decreased with a decrease in probe fragment length (from 1,860 to 735 bases), indicating that many conserved sequences in the chloroplast genome are separated by divergent sequences on a rather fine scale. Despite differences observed in levels of homology with the hydroxylapatite assay, S1 nuclease analysis of heteroduplexes showed that outside of the pea family the extent of sequence relatedness between the probe and various heterologous DNAs is approximately the same: 30%. In our interpretation, the fundamental changes in the chloroplast genome during angiosperm evolution involved the rearrangement of this 30% with respect to the more rapidly changing sequences of the genome. These rearrangements may have been more extensive in dicotyledons than in monocotyledons. We have estimated the amount of conserved and divergent DNA interspersed between one another.From the reassociation experiments, determinations were made of the percentage of chloroplast DNA in total DNA extracts from different higher plants; this value remained relatively constant when compared with the large variation in the diploid genome size of the plants.

Journal Article↗

PubMed1979

Changes in Chloroplast DNA Levels during Development of Pea (Pisum sativum).

Determinations were made of the percentage of chloroplast DNA (ct DNA) in total cell DNA isolated from shoots of pea at different stages of development. Labeled pea ct DNA was reassociated with a high concentration of total DNA; the percentage of ct DNA was estimated by comparing the rate of reassociation of this reaction with that of a model reaction containing a known concentration of unlabeled ct DNA. The maximum change in ct DNA content was from 1.3% of total DNA in young shoots to 7.3% in fully greened shoots. Analyses were also performed on DNA from embryos, etiolated tissue, roots, and leaves. The first leaf set to develop in pea was excised over a growth period of 8 days during which leaf length increased from 4 to 12 millimeters. Young leaves contained about 8% ct DNA; in fully greened leaves the level of ct DNA approached 12%, equivalent to as many as 9,575 copies of ct DNA per cell. Root tissue contained only 0.4% ct DNA.

Journal Article↗