A Mads-Box Homologue in Ustilago Maydis Regulates the Expression of Pheromone-Inducible Genes but Is Nonessential

Mating and pathogenic development in the smut fungus Ustilago maydis are controlled by a pheromone/receptor system and two homeodomain proteins, bEp and bWp, which form heterodimers in nonallelic combinations. We describe the isolation of a gene, umc1, encoding a MADS-box protein, which displays significant similarity to the Saccharomyces cerevisiae MCM1 gene. umc1 complemented the viability defect of yeast mcm1 mutants. In U. maydis, umc1 deletion mutants were viable and pathogenic development was unaffected. Nevertheless, the basal expression levels of several pheromone-inducible genes were significantly reduced leading to an attenuated mating reaction. In contrast to S. cerevisiae, where Mcm1p plays a crucial role in the cell-type specific expression of a- and α-specific genes, the U. maydis umc1 gene appears to have only a modulatory effect on the expression of mating type-specific genes.     

Respiratory function of velopharyngeal constrictor muscles during wakefulness in normal adults

Launois, Sandrine H., Judy Tsui, and J. Woodrow Weiss.Respiratory function of velopharyngeal constrictor muscles during wakefulness in normal adults. J. Appl.Physiol. 82(2): 584-591, 1997.The levator velipalatini (LVP) and the superior pharyngeal constrictor (SPC) influencevelopharyngeal patency and soft palate position, but their behaviorduring respiration is incompletely characterized. To further clarifytheir respiratory function, we recorded electromyographic activity(EMG) in the LVP and the SPC in awake normal subjects breathing orally.EMG data were obtained in six subjects for the LVP and in nine subjectsfor the SPC. EMG activity and timing and ventilation were measuredduring isocapnic hypoxia and hyperoxic hypercapnia. Phasic EMG activitywas inconsistently present during unstimulated oral breathing. Timingof EMG phasic activity was variable for both muscles. Peak LVP activitywas mainly or exclusively expiratory in three of six subjects. Peak SPCactivity was mainly or exclusively expiratory in five of nine subjects.With chemostimulation, recruitment of phasic activity was observed inthe LVP in four of six subjects and in the SPC in five of ninesubjects. Tonic activity increased in four of six subjects for the LVPand in three of nine subjects for the SPC. However, the response wasalinear, and intersubject as well as breath-to-breath variability wassubstantial. In conclusion, LVP and SPC are characterized by the highinter- and intrasubject variability of EMG activity, timing ofactivation, and response to chemostimulation.

     

Amino acid concentrations and selected enzyme activities in rat auditory,olfactory, and visual systems

Homogenates of specific brain regions of three sensory systems (auditory, olfactory, and visual) were prepared from pigmented Long-Evans Hooded rats and assayed for amino acid concentrations and activities of glutaminase, aspartate aminotransferase (total, cytosolic, and, by difference, mitochondrial), malate dehydrogenase, lactate dehydrogenase, and choline acetyltransferase. Comparing the quantitative distributions among regions revealed significant correlations between AAT and aspartate, between glutaminase and glutamate, between glutamate and glutamine, and between AAT plus glutaminase, or glutaminase alone, and the sum of aspartate, glutamate, and GABA, suggesting a metabolic pathway involving the synthesis of a glutamate pool as precursor to aspartate and GABA. Of the inhibitory transmitter amino acids, GABA concentrations routinely exceeded those of glycine, but glycine concentrations were relatively high in brainstem auditory structures.     

Junction formation in aggregated embryonal carcinoma cells

Under the action of supplemental calcium, H6 mouse embryonal carcinoma cell aggregates undergo compaction, a morphological phenomenon similar to mouse embryonic compaction. Formation of various types of cell junctions, especially gap junctions, is associated with compaction of the embryo and we sought to analyze the pattern of junction formation during aggregation and compaction of H6 cells. At 24 hr of aggregation, gap junctions were abundant in both uncompacted and compacted aggregates but quantitative analysis of freeze fracture replicas of these junctions showed a 20-fold increase in the size of the largest gap junctions in compacted aggregates. Such a difference in size could even be detected at 12 hr of aggregation. Tight junctions were not normally formed in 12 hr aggregates but initial stages of tight junction formation could be noticed in 12 hr compacted aggregates. More definitive tight junctions and desmosomes were evident only after 48 hr of aggregation. Thus we have observed that both uncompacted and compacted aggregates can form gap junctions at similar frequencies, suggesting that cell flattening, which contributes to the compacted morphology, is not a requisite for gap junctions. Likewise, generation of the compacted morphology seems to be independent of gap junction formation. This supports the idea that compaction in embryonal carcinoma cells results from calcium-induced cell flattening, probably through the mobilization of cytoskeletal elements. Calcium-dependent features of H6 cell aggregation and compaction enables the independent analysis of separate steps in compaction.     

Molecular basis of heavy-chain class switching and switch region deletion in an Abelson virus-transformed cell line.

We demonstrated that a subclone of an Abelson murine leukemia virus-transformed B-lymphoid cell line switched from mu to gamma 2b expression in vitro, by the classical recombination-deletion mechanism. In this line, the expressed VHDJH region and the C gamma 2b constant region gene were juxtaposed by a recombination event which linked the highly repetitive portions of the S mu and S gama 2b regions and resulted in the loss of the C mu gene from the intervening region. An additional recombination event in this subclone involved an internal deletion in the S mu region of the expressed (switched) allele. One end of this deletion occurred very close to the switch recombination point. Despite the recombination-deletion mechanism of switching, the gamma 2b-producing line retained two copies of the C mu gene and two copies of the sequence just 5' to the S gamma 2b recombination point. The possible significance of the retention of these sequences to the mechanism of class switching is discussed.     

The effect of sugars on (pro)insulin biosynthesis

Rates of incorporation of [4,5-(3)H]leucine into insulin plus proinsulin, designated ;(pro)insulin', and total protein in rat pancreatic islets were measured. Glucose stimulates rates of total protein and (pro)insulin biosynthesis, but (pro)insulin biosynthesis is stimulated preferentially. Mannose and N-acetylglucosamine also stimulate (pro)insulin and total protein biosynthesis; inosine and dihydroxyacetone stimulate (pro)insulin biosynthesis specifically. Fructose does not stimulate (pro)insulin biosynthesis when tested alone, but does so in the presence of low concentrations of glucose, mannose or N-acetylglucosamine. Many glucose analogues do not stimulate (pro)insulin biosynthesis. Mannoheptulose inhibits synthesis of (pro)insulin and total protein stimulated by glucose or mannose but not by dihydroxyacetone, inosine or N-acetylglucosamine; phloretin (9mum) inhibits N-acetylglucosamine-stimulated (pro)insulin biosynthesis preferentially. The data are in agreement with the view that the same glucose-sensor mechanism may control both insulin release and biosynthesis, and ;substrate-site' model is suggested. The threshold for stimulation of biosynthesis of (pro)insulin and total protein is lower than that found for glucose-stimulated insulin release; moreover the biosynthetic response to an elevation of glucose concentration is slower than that found for insulin release. The physiological implication of these findings is discussed. Caffeine and isobutylmethylxanthine, at concentrations known to increase islet 3':5'-cyclic AMP and potentiate glucose-induced insulin release, were without effect on rates of glucose-stimulated (pro)insulin biosynthesis.     

Specificity of two isolated wheat carboxypeptidases

The substrate specificity of two purified carboxypeptidases from germinated wheat has been examined. Both enzymes were active on a wide variety of carbobenzoxy substituted peptides but inactive with unsubstituted dipeptides. Neither enzyme was active upon endoprotease or amidase substrates and only low levels of esterase activity were evident. In time course studies, both enzymes gave rapid non-specific sequential release of amino acids, including proline, from the carboxyterminal of proteins and polypeptides of known amino acid sequence.     

Nucleotide sequence of Rattus norvegiens mitochondrial DNA that includes the genes for tRNAile, tRNAgln and tRNAf-met

The nucleotide sequence of a segment of mtDNA from Rattus norvegiens (rat) which contains the genes for tRNA^ile, tRNA^gl and tRNA^f-met has been determined. A detailed comparison has been made between this sequence and the corresponding sequences of mouse, human and bovine mtDNAs with regard to the primary and secondary structure of the tRNA genes, the regions connecting the tRNA genes, and the regions flanking the tRNA genes which code for the carboxyl terminus of URF-1 and the amino terminus of URF-2. No differences were found in the nucleotide sequences of the genes for tRNA^ile, tRNA^gln and tRNA^f-met in mtDNAs from three different female lines of rats (SASCO-1, SASCO-2 and Wild-UT) that differ by substitutions of 0.8% to 1.8% of their total nucleotides.