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Biomedical subjects

A Mant

Publications and source records attributed to A Mant.

At least 37 records · Page 2Linked to original sources
PubMed1999

Characterisation of an Arabidopsis thaliana cDNA encoding a novel thylakoid lumen protein imported by the delta pH-dependent pathway.

An Arabidopsis thaliana (L.) Heynh. cDNA encoding a novel 16-kDa protein (P16) of the chloroplast thylakoid lumen has been characterised. The function of the protein is unknown but it shares some sequence similarity with alpha allophycocyanins. P16 is synthesised with a bipartite, lumen-targeting presequence, and import experiments demonstrated that this protein follows the delta pH-dependent pathway. Analysis of the thylakoid transfer peptide revealed two unusual features. Firstly, the key targeting determinant is predicted to be a twin-arginine followed by a highly hydrophobic residue two residues later, rather than at the third position as in most transfer peptides. Secondly, the C-terminal domain of the transfer peptide contains multiple charged residues which may help to prevent mistargeting by the Sec-type protein translocase.

Amino Acid Sequence↗
PubMed1999

BUNDLE SHEATH DEFECTIVE2, a novel protein required for post-translational regulation of the rbcL gene of maize.

The Bundle sheath defective2 (Bsd2) gene is required for ribulose-1, 5-bisphosphate carboxylase/oxygenase (Rubisco) accumulation in maize. Using a Mutator transposable element as a molecular probe, we identified a tightly linked restriction fragment length polymorphism that cosegregated with the bsd2-conferred phenotype. This fragment was cloned, and sequences flanking the Mutator insertion were used to screen a maize leaf cDNA library. Using a full-length cDNA clone isolated in this screen, we show that an abundant 0.6-kb transcript could be detected in wild-type plants but not in bsd2-m1 plants. This 0.6-kb transcript accumulated to low levels in plants carrying an allele derived from bsd2-m1 that conditions a less severe mutant phenotype. Taken together, these data strongly suggest that we have cloned the Bsd2 gene. Sequence analysis of the full-length cDNA clone revealed a chloroplast targeting sequence and a region of homology shared between BSD2 and the DnaJ class of molecular chaperones. This region of homology is limited to a cysteine-rich Zn binding domain in DnaJ believed to play a role in protein-protein interactions. We show that BSD2 is targeted to the chloroplast but is not involved in general photosynthetic complex assembly or protein import. In bsd2 mutants, we could not detect the Rubisco protein, but the chloroplast-encoded Rubisco large subunit transcript (rbcL) was abundant and associated with polysomes in both bundle sheath and mesophyll cells. By characterizing Bsd2 expression patterns and analyzing the bsd2-conferred phenotype, we propose a model for BSD2 in the post-translational regulation of rbcL in maize.

Amino Acid Sequence↗
PubMed1999

Incorporating evidence based medicine (EBM) into general practice.

BACKGROUND: The increased application of evidence based medicine (EBM) to health care practice has been endorsed in national health policy. This paper focuses on what EBM means for GPs. OBJECTIVES: To present the outcomes of engaging practising GPs in applying EBM principles to a general practice scenario. DISCUSSION: Caution about the potential for misuse of EBM has been voiced by GPs based on the biopsychosocial model of general practice and concerns about the limited utility of largely biomedical evidence in general practice. The EBM process begins with converting information needs into questions, but this first step presupposes that the doctor has obtained a good history including eliciting any hidden agenda. It is important to recognise the context in which people's health issues and problems arise, the paucity of evidence that is derived within the biopsychosocial model of general practice, and the difficulties that GPs face in accessing evidence.

Adult↗
PubMed1998

Characterisation of an Arabidopsis cDNA encoding a thylakoid lumen protein related to a novel 'pentapeptide repeat' family of proteins.

We have cloned an Arabidopsis cDNA encoding a novel thylakoid lumen protein, P17.4, that has been previously isolated from lumen extracts of spinach chloroplasts. The protein is synthesised with a bipartite presequence containing a Sec-type lumen-targeting signal peptide and the precursor protein is imported into the lumen of pea chloroplasts. The encoded protein is homologous to an Anabaena protein that is essential for correct glycolipid localisation, and is also related to at least 16 unassigned open reading frames in Synechocystis. This family of proteins is characterised by the presence of numerous pentapeptide repeats with the consensus structure AXLXX, and its members are predicted to be located in the cytosol, plasma membrane and periplasm/lumen. P17.4 is therefore the first higher plant member of an extended family of putative cyanobacterial proteins that may serve important roles in lipid transport or assembly.

Amino Acid Sequence↗
PubMed1998

Sec/SRP-independent insertion of two thylakoid membrane proteins bearing cleavable signal peptides.

Two imported thylakoid membrane proteins, PSII-X and PSII-W, are synthesised with cleavable N-terminal signal peptides that closely resemble those of Sec-dependent lumenal proteins. In this report we have reconstituted the insertion of pre-PSII-X and pre-PSII-W into isolated thylakoids. We show that insertion does not require either nucleoside triphosphates or stromal extracts, both of which are required for Sec- and signal recognition particle (SRP)-dependent targeting mechanisms. Insertion is furthermore unaffected by protease treatments that destroy the known protein translocation apparatus in the thylakoid membrane. We conclude that these membrane proteins are inserted by an unusual Sec/SRP-independent mechanism that probably resembles that used by CFoII, and we discuss possible parallels with the biogenesis of phage M13 procoat.

Chloroplasts↗
PubMed1998

An Arabidopsis cDNA encodes an apparent polyprotein of two non-identical thylakoid membrane proteins that are associated with photosystem II and homologous to algal ycf32 open reading frames.

We have characterised an Arabidopsis thaliana cDNA homologous to the ycf32 open reading frames present in the Synechocystis genome and the plastid genomes of several eukaryotic algae. The predicted protein is also homologous to a novel protein reported to be associated with photosystem II. The protein is synthesised as a 23 kDa precursor with an N-terminal presequence that appears to be bipartite in structure, and the protein is targeted into the thylakoid membrane of pea chloroplasts. Although the Ycf32 presequence contains an apparent signal peptide, we find that this protein is not imported by either of the standard Sec- or deltapH-dependent pathways. The mature protein is also unusual in two respects. First, there are two distinct, non-identical copies of typical single-span Ycf32 sequences in the Arabidopsis sequence, separated by an additional hydrophobic region. Secondly, the imported protein runs as a doublet of 6 kDa and 7 kDa polypeptides whereas the mature protein is predicted to be 14 kDa. We speculate that the protein undergoes further maturation once inserted into the thylakoid membrane to yield two separate Ycf32-like polypeptides.

Amino Acid Sequence↗
PubMed1998

Making sense of the results of your research.

The key to making the most of your results lies in clarifying your plan of analysis first. Cleaning your data is also essential. Make sure you have help and that you give credit to any funding sources.

Humans↗
PubMed1998

Multiple pathways for the targeting of thylakoid proteins in chloroplasts.

The assembly of the photosynthetic apparatus requires the import of numerous cytosolically synthesised proteins and their correct targeting into or across the thylakoid membrane. Biochemical and genetic studies have revealed the operation of several targeting pathways for these proteins, some of which are used for thylakoid lumen proteins whereas others are utilised by membrane proteins. Some pathways can be traced back to the prokaryotic ancestors of chloroplasts but at least one pathway appears to have arisen in response to the transfer of genes from the organelle to the nucleus. In this article we review recent findings in this field that point to the operation of a mechanistically unique protein translocase in both plastids and bacteria, and we discuss emerging data that reconcile the remarkable variety of targeting pathways with the natures of the substrate precursor proteins.

Amino Acid Sequence↗
PubMed1997

Antibiotic use in the Australian community, 1990-1995.

OBJECTIVE: To determine the pattern of antibiotic use in the Australian community, 1990-1995, and compare it with the pattern in other developed countries. DESIGN: Survey of data from the national database on drugs dispensed in Australia (1990-1995), an international database on retail drug sales (1985-1994), and Australian prescriber surveys (1994, 1995). MAIN OUTCOME MEASURES: National and international retail sales of oral antibiotics (defined daily doses [DDDs]/1000 population/day) and antibiotic prescriptions dispensed through community pharmacies by drug type; antibiotic prescribing profiles for common conditions. RESULTS: Antibiotic use in Australia remained steady between 1990 and 1995, with an estimated 24.7 DDDs/1000 population/day dispensed through community pharmacies in 1990 and 24.8 DDDs/1000 population/day in 1995. Amoxycillin, although declining in use, remained the most dispensed antibiotic. Compared with the other countries surveyed, Australia had the highest percentage use of tetracyclines, such as doxycycline, and the lowest percentage use of fluoroquinolones. Use of trimethoprim-sulfamethoxazole and flucloxacillin declined in Australia. In new cases of upper respiratory tract infection or pharyngitis, an antibiotic prescription was recorded for 57% of urban patient encounters and 73% of rural patient encounters. CONCLUSIONS: Antibiotic use in Australia is high, as in many other developed countries, but did not increase between 1990 and 1995. The overall profile of antibiotic use in Australia by drug class was similar to that in the United Kingdom. Antibiotics were still commonly prescribed for upper respiratory tract infection (which is usually viral), more commonly by rural than by urban general practitioners.

Administration, Oral↗
PubMed1997

Unusual characteristics of amino-terminal and hydrophobic domains in nuclear-encoded thylakoid signal peptides.

Thylakoid transfer signals carry information specifying translocation by either a Sec- or delta pH-dependent protein translocator in the chloroplast thylakoid membrane, yet all resemble classical signal peptides in overall structural terms. Comparison of known transfer signals reveals two differences: (a) signals for the delta pH-driven system invariably contain a critical twin-arginine (Arg-Arg) motif prior to the hydrophobic (H) domain, whereas known Sec-dependent signals contain lysine, and (b) the H-domains of Sec-dependent signals are generally longer. Previous work has shown that a twin-Arg motif before the H-domain is critical for targeting by the delta pH-dependent pathway; in this report we show that the charge characteristics of this region are not important for sorting by the Sec pathway. Twin-Lys, twin-Arg or single Arg are all acceptable to the Sec system, although single Lys/Arg is preferred. The single Lys in pre-plastocyanin can even be replaced by an uncharged residue without apparent effect. We have also generated a pre-plastocyanin mutant containing an H-domain which, in terms of hydropathy profile, is identical to that of a delta pH-dependent protein. This mutant is also transported efficiently by the Sec system, demonstrating that hydrophobicity per se is not a key sorting determinant. However, the characteristics of the H-domain may be important in avoiding a different form of mis-targeting: to the endoplasmic reticulum. Thylakoid signal peptides have undergone substantial structural changes during the evolution of the chloroplast from endosymbiotic cyanobacterium: plastid-encoded and cyanobacterial signals contain H-domains that are highly hydrophobic and enriched in Leu and aromatic residues, whereas nuclear-encoded counterparts are Ala-rich and far less hydrophobic. We speculate that this trend may reflect a need to avoid mistargeting through recognition by cytosolic signal recognition particle, which preferentially interacts with more hydrophobic signal peptides.

Amino Acid Sequence↗