Molecular biology of chloroplast biogenesis: gene expression, protein import and intraorganellar sorting

The chloroplast is the hallmark organelle of plants. It performs photosynthesis and is therefore required for photoautotrophic plant growth. The chloroplast is the most prominent member of a family of related organelles termed plastids which are ubiquitous in plant cells. Biogenesis of the chloroplast from undifferentiated proplastids is induced by light. The generally accepted endosymbiont hypothesis states that chloroplasts have arisen from an internalized cyanobacterial ancestor. Although chloroplasts have maintained remnants of the ancestral genome (plastome), the vast majority of the genes encoding chloroplast proteins have been transferred to the nucleus. This poses two major challenges to the plant cell during chloroplast biogenesis: First, light and developmental signals must be interpreted to coordinately express genetic information contained in two distinct compartments. This is to ensure supply and stoichiometry of abundant chloroplast components. Second, developing chloroplasts must efficiently import nuclear encoded and cytosolically synthesized proteins. A subset of proteins, including such encoded by the plastome, must further be sorted to the thylakoid compartments for assembly into the photosynthetic apparatus. Received 1 September 2000; received after revision 27 October 2000; accepted 1 November 2000     

T-cell signal transduction and the role of protein kinase C

The T lymphocyte has a vital part to play in maintaining the host response to bacterial and viral infection and also appears to play a key pathological role in autoimmune diseases such as rheumatoid arthritis. In this review, we summarize the signalling pathways which trigger antigen-driven T-cell proliferation and examine the evidence which suggests that protein kinase C (PKC) is fundamental to this process. Finally, we discuss the therapeutic potential that PKC inhibitors may have in the treatment of autoimmune disease. Received 31 March 1998; received after revision 19 May 1998; accepted 19 May 1998     

Regulation of mitochondrial oxidative phosphorylation by second messenger-mediated signal transduction mechanisms

The mitochondrial oxidative phosphorylation system is responsible for providing the bulk of cellular ATP molecules. There is a growing body of information regarding the regulation of this process by a number of second messenger-mediated signal transduction mechanisms, although direct studies aimed at elucidating this regulation are limited. The main second messengers affecting mitochondrial signal transduction are cAMP and calcium. Other second messengers include ceramide and reactive oxygen species as well as nitric oxide and reactive nitrogen species. This review focuses on available data on the regulation of the mitochondrial oxidative phosphorylation system by signal transduction mechanisms and is organised according to the second messengers involved, because of their pivotal role in mitochondrial function. Future perspectives for further investigations regarding these mechanisms in the regulation of the oxidative phosphorylation system are formulated. Received 11 December 2005; received after revision 14 January 2006; accepted 6 February 2006     

Family I.3 lipase: bacterial lipases secreted by the type I secretion system

Based on the classification of bacterial lipolytic enzymes, family I.3 lipase is a member of the large group of Gram-negative bacterial true lipases. This lipase family is distinguished from other families not only by the amino acid sequence, but also by the secretion mechanism. Lipases of family I.3 are secreted via the well-known type I secretion system. Like most of proteins secreted via this system, family I.3 lipases are composed of two domains with distinct yet related functions. Recent years have seen an increasing amount of research on this lipase family, in terms of isolation, secretion mechanism, as well as biochemical and biophysical studies. This review describes our current knowledge on the structure-function relationships of family I.3 lipase, with an emphasis on its secretion mechanism. Received 18 April 2006; received after revision 3 July 2006; accepted 24 August 2006