The mitochondrial gene encoding ribosomal protein S12 has been translocated to the nuclear genome in Oenothera.

The Oenothera mitochondrial genome contains only a gene fragment for ribosomal protein S12 (rps12), while other plants encode a functional gene in the mitochondrion. The complete Oenothera rps12 gene is located in the nucleus. The transit sequence necessary to target this protein to the mitochondrion is encoded by a 5'-extension of the open reading frame. Comparison of the amino acid sequence encoded by the nuclear gene with the polypeptides encoded by edited mitochondrial cDNA and genomic sequences of other plants suggests that gene transfer between mitochondrion and nucleus started from edited mitochondrial RNA molecules. Mechanisms and requirements of gene transfer and activation are discussed.     

Enhanced production of cellulase usingAcidothermus cellulyticus in fed-batch culture

Summary Fed-batch fermentations of Acidothermus cellulolyticus utilizing mixtures of cellulose and sugars were investigated for potential improvements in cellulase enzyme production. In these fermentations, we combined cellulose from several sources with various simple sugars at selected concentrations. The best source of cellulose for cellulase production was found to be ball-milled Solka Floc at 15 g/l. Fed-batch fermentations with cellobiose and Solka Floc increased cell mass only slightly, but succeeded in significantly enhancing cellulase synthesis compared to batch conditions. Maximum cellulase activities obtained from fermentations initiated with 2.5 g cellobiose/l and 15 g Solka Floc/l were 0.187 units (U)/ml, achieved by continuous feeding to maintain <0.1 g cellobiose/l, and 0.215 U/ml using the same initial medium when 2.5 g cellobiose/l was step-fed after the sugar was nearly consumed. In batch, dual-substrate systems consisting of simple sugars with Solka Floc, substrate inhibition was evident in terms of specific growth rates, specific productivity values, and maximum enzyme yields. Limiting concentrations of glucose or sucrose at 5 g/l, and cellobiose at 2.5 g/l, in the presence of Solka Floc, yielded cellulase activities of 0.134, 0.159, and 0.164 U/ml, respectively. Offprint requests to: M. E. Himmel     

The nuclear coded mitoribosomal proteins YmL27 and YmL31 are both essential for mitochondrial function in yeast.

Using synthetic oligonucleotides deduced from the N-terminal amino acid sequence of purified mitoribosomal protein (mt r-protein) YmL27, the corresponding nuclear gene MRP-L27 of the yeast Saccharomyces cerevisiae has been cloned and sequenced. The MRP-L27 gene codes for 146 amino acids and is located on chromosome X. The mature YmL27 protein consists of 130 amino acids - after cleaving the putative mitochondrial signal peptide - with a net charge of +17 and a calculated relative molecular mass of 14,798 Da. The YmL27 protein as well as the yeast mitoribosomal protein YmL31, which had been characterized and its gene (MRP-L31) cloned previously, is essential for mitochondrial function as shown by the inability of gene disrupted mutants for the MRP-L27 or MRP-L31 genes to grow on non-fermentable carbon sources.     

Organosolv pretreatment for enzymatic hydrolysis of poplars: I. Enzyme hydrolysis of cellulosic residues

Aspen (Populus tremuloides) and black cottonwood (Populus trichocarpa) organosolv pulps produced in a wide range of solvent composition (between 30 and 70% by volume of methanol) and catalysts (H(2)SO(4) and H(3)PO(4)) such that the cooking liquor pH 相似文献   

Localization of sequences regulating ancestral and acquired sites of esterase6 activity in Drosophila melanogaster

We have broadly defined the DNA regions regulating esterase6 activity in several life stages and tissue types of D. melanogaster using P- element-mediated transformation of constructs that contain the esterase6 coding region and deletions or substitutions in 5' or 3' flanking DNA. Hemolymph is a conserved ancestral site of EST6 activity in Drosophila and the primary sequences regulating its activity lie between -171 and -25 bp relative to the translation initiation site: deletion of these sequences decrease activity approximately 20-fold. Hemolymph activity is also modulated by four other DNA regions, three of which lie 5' and one of which lies 3' of the coding region. Of these, two have positive and two have negative effects, each of approximately twofold. Esterase6 activity is present also in two male reproductive tract tissues; the ejaculatory bulb, which is another ancestral activity site, and the ejaculatory duct, which is a recently acquired site within the melanogaster species subgroup. Activities in these tissues are at least in part independently regulated: activity in the ejaculatory bulb is conferred by sequences between -273 and -172 bp (threefold decrease when deleted), while activity in the ejaculatory duct is conferred by more distal sequences between -844 and -614 bp (fourfold decrease when deleted). The reproductive tract activity is further modulated by two additional DNA regions, one in 5' DNA (-613 to -284 bp; threefold decrease when deleted) and the other in 3' DNA (+1860 to +2731 bp; threefold decrease when deleted) that probably overlaps the adjacent esteraseP gene. Collating these data with previous studies suggests that expression of EST6 in the ancestral sites is mainly regulated by conserved proximal sequences while more variable distal sequences regulate expression in the acquired ejaculatory duct site.      

Phylogenetic diversification of immunoglobulin genes and the antibody repertoire

Immunoglobulins are encoded by a large multigene system that undergoes somatic rearrangement and additional genetic change during the development of immunoglobulin-producing cells. Inducible antibody and antibody-like responses are found in all vertebrates. However, immunoglobulin possessing disulfide-bonded heavy and light chains and domain-type organization has been described only in representatives of the jawed vertebrates. High degrees of nucleotide and predicted amino acid sequence identity are evident when the segmental elements that constitute the immunoglobulin gene loci in phylogenetically divergent vertebrates are compared. However, the organization of gene loci and the manner in which the independent elements recombine (and diversify) vary markedly among different taxa. One striking pattern of gene organization is the "cluster type" that appears to be restricted to the chondrichthyes (cartilaginous fishes) and limits segmental rearrangement to closely linked elements. This type of gene organization is associated with both heavy- and light-chain gene loci. In some cases, the clusters are "joined" or "partially joined" in the germ line, in effect predetermining or partially predetermining, respectively, the encoded specificities (the assumption being that these are expressed) of the individual loci. By relating the sequences of transcribed gene products to their respective germ-line genes, it is evident that, in some cases, joined-type genes are expressed. This raises a question about the existence and/or nature of allelic exclusion in these species. The extensive variation in gene organization found throughout the vertebrate species may relate directly to the role of intersegmental (V<==>D<==>J) distances in the commitment of the individual antibody-producing cell to a particular genetic specificity. Thus, the evolution of this locus, perhaps more so than that of others, may reflect the interrelationships between genetic organization and function.      

Conjugative plasmid transfer in gram-positive bacteria.

Conjugative transfer of bacterial plasmids is the most efficient way of horizontal gene spread, and it is therefore considered one of the major reasons for the increase in the number of bacteria exhibiting multiple-antibiotic resistance. Thus, conjugation and spread of antibiotic resistance represents a severe problem in antibiotic treatment, especially of immunosuppressed patients and in intensive care units. While conjugation in gram-negative bacteria has been studied in great detail over the last decades, the transfer mechanisms of antibiotic resistance plasmids in gram-positive bacteria remained obscure. In the last few years, the entire nucleotide sequences of several large conjugative plasmids from gram-positive bacteria have been determined. Sequence analyses and data bank comparisons of their putative transfer (tra) regions have revealed significant similarities to tra regions of plasmids from gram-negative bacteria with regard to the respective DNA relaxases and their targets, the origins of transfer (oriT), and putative nucleoside triphosphatases NTP-ases with homologies to type IV secretion systems. In contrast, a single gene encoding a septal DNA translocator protein is involved in plasmid transfer between micelle-forming streptomycetes. Based on these clues, we propose the existence of two fundamentally different plasmid-mediated conjugative mechanisms in gram-positive microorganisms, namely, the mechanism taking place in unicellular gram-positive bacteria, which is functionally similar to that in gram-negative bacteria, and a second type that occurs in multicellular gram-positive bacteria, which seems to be characterized by double-stranded DNA transfer.     

The NADH-binding subunit of respiratory chain complex I is nuclear-encoded in plants and identified only in mitochondria

In higher plants, genes for subunits of respiratory chain complex I (NADH:ubiquinone oxidoreductase) have so far been identified solely in organellar genomes. At least nine subunits are encoded by the mitochondrial DNA and 11 homologues by the plastid DNA. One of the 'key' components of complex I is the subunit binding the substrate NADH. The corresponding gene for the mitochondrial subunit has now been cloned and identified in the nuclear genome from potato ( Solanum tuberosum ). The mature protein consists of 457 amino acids and is preceded by a mitochondrial targeting sequence of 30 amino acids. The protein is evolutionarily related to the NADH-binding subunits of complex I from other eukaryotes and is well conserved in the structural domains predicted for binding the substrate NADH, the FMN and one iron-sulphur cluster. Expression examined in different potato tissues by Northern blot analysis shows the highest steady-state mRNA levels in flowers.
Precursor proteins translated in vitro from the cDNA are imported into isolated potato mitochondria in a ΔΨ-dependent manner. The processed translation product has an apparent molecular mass of 55 kDa, identical to the mature protein present in the purified plant mitochondrial complex I. However, the in-vitro translated protein is not imported into isolated chloroplasts. To further investigate whether the complex I-like enzyme in chloroplasts contains an analogous subunit for binding of NAD(P)H, different plastid protein fractions were tested with a polyclonal antiserum directed against the bovine 51 kDa NADH-binding subunit. In none of the different thylakoid or stroma protein fractions analysed were specific crossreactive polypeptides detected. These results are discussed particularly with respect to the structure of a potential complex I in chloroplasts and the nature of its acceptor site.