var1 Gene on the mitochondrial genome of Torulopsis glabrata

We have cloned and sequenced a region of the Torulopsis glabrata mitochondrial genome homologous to the Saccharomyces cerevisiae var1 gene (var1Sc). An open reading frame that could encode a protein of 339 amino acids was found with 72.7% amino acid and 85.3% nucleotide sequence homology to the S. cerevisiae var1 gene. The T. glabrata gene (var1Tg) is transcribed yielding two stable RNAs, a more abundant 13.5 S RNA and a less abundant 18 S species. We have also identified a candidate for a T. glabrata var1 protein among mitochondrial translation products labeled in isolated mitochondria. The var1Tg gene is even more A + T-rich (93%) than var1Sc (89.6%) and has conserved the strong codon bias of var1Sc. Major differences between the two sequences were found. Significant among these are that no GC clusters are found in var1Tg and the sequences surrounding each of the sites where known polymorphisms exist in var1Sc have deletions at the corresponding sites in var1Tg. These data are discussed with respect to possible origins of these var1 genes and translocation of GC clusters in S. cerevisiae mitochondrial DNA.     

Promoter mutations affecting divergent transcription in the Tn10 tetracycline resistance determinant

The tetracycline resistance determinant in transposon Tn10 consists of two genes, the tetA resistance gene and the tetR repressor gene, that are transcribed from divergent overlapping promoters. We determined the levels of pulse-labeled tet messenger RNA in Escherichia coli strains with the Tn10 tet genes on a multicopy plasmid. Addition of the inducer 5a,6-anhydrotetracycline results in a 270- to 430-fold increase in tetA mRNA and a 35- to 65-fold increase in tetR mRNA. As judged by the relative molar amounts of tetA and tetR mRNA synthesized under maximally inducing conditions, the tetA promoter (tetPA) is 7 to 11 times more active than the two tetR promoters (tetPR1 and tetPR2) combined. We characterized ten mutations in tetPA, including nine single-base-pair substitutions and a 30-base-pair deletion. All of the single-base-pair changes reduce the agreement with the consensus sequence for promoters recognized by E. coli RNA polymerase. Mutations in highly conserved nucleotides result in a 200- to 600-fold reduction in tetPA activity in vivo. Unexpectedly, tetPA mutations reduce by two- to fourfold the combined activity in vivo of tetPR1 and tetPR2, in spite of their locations outside the -35 and -10 regions of tetPR1 and tetPR2. For two tetPA mutations, the negative effect on tetPR activity was also demonstrated in tetR- tetPR-lacZ operon fusion strains, thus eliminating the possibility that it is due to variations in either plasmid copy-number or induction efficiency. The pleiotropic effects of tetPA mutations are discussed in terms of the expectation that the overlapping tet promoters compete for RNA polymerase.     

Genetic reconstruction and functional analysis of the repeating lipoyl domains in the pyruvate dehydrogenase multienzyme complex of Escherichia coli

The dihydrolipoamide acetyltransferase component (E2p) of the pyruvate dehydrogenase complex of Escherichia coli contains three highly homologous sequences of about 100 residues that are tandemly repeated to form the N-terminal half of the polypeptide chain. All three sequences include a lysine residue that is a site for lipoylation and they appear to form independently folded functional domains. These lipoyl domains are in turn linked to a much larger (about 300 residues) subunit-binding domain of the E2p chain that aggregates to form the octahedral inner core of the complex and also contains the acetyltransferase active site. In order to investigate whether individual lipoyl domains play different parts in the enzymic mechanism, selective deletions were made in vitro in the dihydrolipoamide acetyltransferase gene (aceF) so as to excise one or two of the repeating sequences. This was facilitated by the high degree of homology in these sequences, which allowed the creation of hybrid lipoyl domains that closely resemble the originals. Pyruvate dehydrogenase complexes incorporating these genetically reconstructed E2p components were purified and their structures were confirmed. It was found that the overall catalytic activity, the system of active site coupling, and the ability to complement pyruvate dehydrogenase complex mutants, were not significantly affected by the loss of one or even two lipoyl domains per E2p chain. No special role can be attached thus far to individual lipoyl domains. On the other hand, certain genetic deletions affecting the acetyltransferase domain caused inactivation of the complex, highlighting particularly sensitive areas of that part of the E2p chain.     

Nitrification inhibition of added nitrogenous fertilisers by potassium chloride in soil

Summary Inhibitory effect of potassium chloride on nitrification of ammonium sulfate and urea in acid, neutral and calcareous soils was observed in an incubation study. In acidic soil, NO ₃ ^– –N production in soil treated with urea was retarded by addition of KCl. NO ₃ ^– –N concentration was much less even in comparison to control where ammonium sulfate and KCl were added together which might be due to cumulative effect of Cl^– and SO ₄ ^–2 ions. In neutral and calcareous soils, nitrification inhibition was less conspicuous.     

Further Studies on the Nature of Postsynaptic Dopamine Uptake and Metabolism in Rat Striatum: Sodium Dependency and Investigation of a Possible Role for Carrier-Mediated Uptake into Serotonin Neurons

The nature of postsynaptic sites involved in the uptake and metabolism of striatal 3,4-dihydroxyphenylethylamine (dopamine, DA) was investigated. The accumulation of [3H]DA (10(-7) M) into slices of rat striatum was found to be greatly dependent (greater than 99%) on the presence of sodium ion in the incubation medium. However, the formation of the [3H]dihydroxyphenylacetic acid (DOPAC) and [3H]homovanillic acid (HVA) was only partially reduced in the absence of sodium (DOPAC, 27% of control; HVA, 47% of control). Inhibition of carrier-mediated DA neuronal uptake with nomifensine (10(-5) M) significantly decreased DA accumulation (18% of control) and [3H]DOPAC formation (62% of control), but enhanced [3H]HVA production (143% of control). Inhibition of the 5-hydroxytryptamine (5-HT, serotonin) neuronal uptake system with fluoxetine (10(-6) M) or selective 5-HT neuronal lesions with 5,7-dihydroxytryptamine (5,7-DHT) had no effect on [3H]DOPAC or [3H]HVA formed from [3H]DA in the presence or absence of nomifensine. These results demonstrate that the uptake and subsequent metabolism of striatal DA to DOPAC and HVA is only partially dependent on carrier-mediated uptake mechanism(s) requiring sodium ion. These data support our previous findings suggesting a significant role for synaptic glial cell deamination and O-methylation of striatal DA. Further, experiments with fluoxetine or 5,7-DHT suggest that 5-HT neurons do not significantly contribute in the synaptic uptake and metabolism of striatal DA.     

Dopamine Sulfoconjugation in the Rat Brain: Regulation by Monoamine Oxidase

An increase of free 3,4-dihydroxyphenylethylamine (DA, dopamine) in the rat brain such as is found following 3,4-dihydroxyphenylalanine (L-DOPA) administration or an intraventricular injection of free dopamine did not result in DA sulfate formation, despite the presence of phenolsulfotransferase activity in various regions of the brain and the high affinity of DA for this enzyme. However, when rats were pretreated with pargyline, a monoamine oxidase inhibitor, the same treatment with L-DOPA or free DA led to active synthesis of DA sulfate. The increase in DA sulfate was significantly correlated with the degree of monoamine oxidase inhibition and directly proportional to free DA concentrations in the hypothalamus (r = 0.86), striatum (r = 0.54), and brainstem (r = 0.89). The highest ratio of DA sulfate to free DA was found in the hypothalamus, suggesting that sulfoconjugation is most active in this region. Prior treatment of rats with 6-hydroxydopamine did not decrease DA sulfate concentrations, indicating that sulfoconjugation occurs most likely in extraneuronal tissues not destroyed by the neurotoxin. The results are compatible with the notion that phenolsulfotransferase may be highly compartmentalized and that inhibition of monoamine oxidase allows the newly generated free DA to become accessible to the sulfoconjugating enzyme, resulting in increase in DA sulfation.     

Difference in the Pattern of Soluble Proteins from Rat Brain Regions

The electrophoretic pattern of soluble proteins from seven rat brain regions (amygdala, cerebellum, corpus striatum, cortex, hypothalamus, medulla, and midbrain) was examined by sodium dodecyl sulphate-polyacrylamide gel electrophoresis. Although the number of protein bands (36) was identical in all brain regions studied, there were differences in their relative densities, the greatest variation occurring in the low-molecular-weight region of the electrophoretogram. The bulk of the soluble proteins had molecular weights between 23,000 and 90,000 daltons. The medulla and amygdala showed the greatest range of protein band concentration. A large number of protein bands in the midbrain and corpus striatum showed a greater concentration of protein compared to the same bands in the other regions. A protein band that migrated with the same characteristic as albumin was found. It was consistently high in all regions, the midbrains showing a 1.5-fold greater concentration compared to other regions. Linear regression analysis of wet weight of regional brain tissue against protein concentration yielded a regression coefficient (r2) of 0.77. Midbrain and corpus striatum showed a relatively higher protein concentration: weight ratio than other regions.