Frequent derepression of G6PD and HPRT on the marsupial inactive X chromosome associated with cell proliferation in vitro

X chromosome dosage compensation in Marsupials is like that in eutherian mammals except that the paternal X chromosome is always inactive, and silence of this chromosome is not well maintained. We previously showed that the unstable inactivation of the paternal G6PD allele is associated with the lack of DNA methylation in the 5' CpG cluster. Even though this CpG island is unmethylated, the paternal allele (marked by an enzyme variant) is at least partially and often severely repressed in most tissues of the opossum, so that factors other than methylation must inactivate the locus. Here we report that when cell cultures are established from these tissues, the silent G6PD locus is depressed. Although often complete, the extent of derepression differs among tissues and within different cell types in the same tissue, and is not accompanied by obvious changes in the pattern of chromosome replication. Studies of the HPRT locus in these cells show that the paternal HPRT allele also derepresses in cultured cells. These observations suggest that without DNA methylation to maintain the silence of the locus, tissue or cell-specific factors act to repress the silent locus, but are unable to maintain inactivity through cell division, or are lost as cells proliferate in culture.     

Signal peptidase can cleave inside a polytopic membrane protein

The signal peptides of most proteins targeted to the endoplasmic reticulum are specifically cleaved by signal peptidase. Although potential cleavage sites occur frequently in polytopic proteins after membrane-spanning segments, processing is restricted to the first hydrophobic domain, suggesting that signal peptidase might not have access to subsequently translocated, internal domains. To test this hypothesis, we replaced the third transmembrane segment of an artificial threefold membrane-spanning protein by a sequence which is normally an amino-terminal signal. Upon in vitro translation and insertion into microsomes, efficient cleavage at this sequence was observed, thus demonstrating the ability of signal peptidase to cleave within polytopic membrane proteins.     

Isolation and structure of corazonin, a cardioactive peptide from the American cockroach

Corazonin, a new cardioaccelerating peptide, has been isolated from the corpora cardiaca of the American cockroach, Periplaneta americana, and its structure determined to be Glp-Thr-Phe-Gln-Tyr-Ser-Arg-Gly-Trp-Thr-Asn-amide. The peptide stimulated heart beat at concentrations as low as 0.2 nM, which makes it the most potent insect cardioactive neuropeptide.     

Glycolipid- and glycoprotein-based blood group A antigen expression in human thrombocytes. A1/A2 difference

Total non-acid glycolipid fractions and total sodium dodecylsulphate (SDS) solubilized protein fractions were isolated from human thrombocytes obtained from single human donors having different blood group A₁/A₂ phenotypes. The blood group A glycolipid antigens were characterized by immunostaining of thin layer plates with different monoclonal anti-A antibodies. The glycoproteins carrying blood group A epitopes were identified by SDS-PAGE and Western blot analysis using a monoclonal anti-A antibody. Blood group A glycolipid antigens were found in both A₁ and A₂ thrombocytes but the A₂ individuals expressed at least ten times less A glycolipids compared to the A₁ individuals. Expression of A type 3/4 chain and small amounts of A type 1 chain glycolipids were seen in thrombocytes of both A₁ and A₂ individuals, while the type 2 chain A glycolipids appeared to be missing from the A₂ thrombocytes. Blood group A reactive glycoproteins were only found in thrombocytes of A₁ individuals and could not be detected in A₂ individuals or a blood group O individual. The major blood group A glycoprotein were found as a double band migrating in the 130 kDa region.Abbreviations SDS sodium dodecyl sulfate - PAGE polyacrylamide gel electrophoresis - HPTLC high performance thin layer chromatography - CBB Coomassie brilliant blue - GVH graft versus host Part of this work was presented at the Xth International Symposium on Glycoconjugates, Jerusalem, Israel. September, 1989.In the short hand designation for glycolipids, the letter indicate blood group determinant, the first numeral, the number of sugar residues, and the second numeral, the type of carbohydrate chain. Thus, A-6-1 means a hexaglycosylceramide with a blood group A determinant based on the type 1 carbohydrate chain.     

Rapid detection of chromosome 16 inversion in acute nonlymphocytic leukemia, subtype M4: regional localization of the breakpoint in 16p

The pericentric inversion of chromosome 16 characteristic for acute nonlymphocytic leukemia, subtype M4, was detected in five patients by means of nonradioactive in situ hybridization of complete cosmids. First, five cosmids situated along the short arm of chromosome 16 were used to map the breakpoint of the inversion distal to the rare folate-sensitive fragile site FRA16A. Then, the use of two cosmids on either side of the breakpoint, combined with a probe specific for the centromeric region of chromosome 16, readily detected the inversion, even in poor metaphase spreads.     

The phylogenic position of Peptococcus niger based on 16S rRNA sequence studies

A 1330 base-pair fragment of a 16S rRNA gene has been amplified, cloned and sequenced. Comparison to other 16S rRNA sequences of eubacteria showed that P. niger represents a deep branch within the subdivision "Gram-positive with Gram-negative cell walls". It is not related to peptostreptococci, representatives of this genus studied so far are more closely related to clostridia.     

5,6,7,8-Tetrahydromethanopterin-dependent enzymes involved in methanogenesis

Abstract In the process of methanogenesis, 5,6,7,8-tetrahydromethanopterin (H₄MPT) is the carrier of the C₁ unit at the formyl through methyl state of reduction. By the transfer of a formyl group from formylmethanofuran, 5-formyl- and 10-formyl-H₄MPT are formed in hydrogenotrophic and methylotrophic organisms, respectively. Cyclohydrolysis of the 5- and 10-formyl derivatives then yields 5,10-methenyl-H₄MPT, which is reduced in two subsequent coenzyme F₄₂₀-dependent reactions to 5-methyl-H₄MPT. Following the transfer of the methyl group to coenzyme M, the substrate of the terminal step in methanogenesis, methylcoenzyme M, is produced. In this paper properties of the enzymes catalyzing the individual H₄MPT-dependent reactions are discussed.     

Effects of training at simulated altitude on performance and muscle metabolic capacity in competitive road cyclists

Differences between the effects of training at sea level and at simulated altitude on performance and muscle structural and biochemical properties were investigated in 8 competitive cyclists who trained for 3-4 weeks, 4-5 sessions/week, each session consisting of cycling for 60-90 min continuously and 45-60 min intermittently. Four subjects, the altitude group (AG), trained in a hypobaric chamber (574 torr = 2300 m above sea level), and the other four at sea level (SLG). Before and after training work capacity was tested both at simulated altitude (574 torr) and at sea level, by an incremental cycle ergometer test until exhaustion. Work capacity was expressed as total amount of work performed. Venous blood samples were taken during the tests. Leg muscle biopsies were taken at rest before and after the training period. AG exhibited an increase of 33% in both sea level and altitude performance, while SLG increased 22% at sea level and 14% at altitude. Blood lactate concentration at a given submaximal load at altitude was significantly more reduced by training in AG than SLG. Muscle phosphofructokinase (PFK) activity decreased with training in AG but increased in SLG. All AG subjects showed increases in capillary density. In conclusion, work capacity at altitude was increased more by training at altitude than at sea level. Work capacity at sea level was at least as much improved by altitude as by sea level training. The improved work capacity by training at altitude was paralleled by decreased exercise blood lactate concentration, increased capillarization and decreased glycolytic capacity in leg muscle.