Cat satellite DNA. Isolation using netropsin with CsCl gradients

The absence of centromeric bands in the karyotype of Felis catus is confirmed. It is also confirmed that no satellite band is visible in CsCl density gradients. However, a satellite is observed both by recentrifuging the fraction of the DNA that bands at high density in CsCl and by using netropsin to enhance the resolution of a CsCl gradient containing total F. catus DNA. The satellite, about 0.5% of total DNA, was isolated by repeated centrifugation in CsCl alone and in CsCl with netropsin. Netropsin was removed and a pure satellite DNA obtained. The reassociation kinetics (C0t1/2 less than 10(-3) M . s) show that the satellite is of the simple sequence type and hence a candidate for centromeric heterochromatin. Its cytological localisation awaits in situ hybridisation experiments.     

Structure—activity relationships in the mutagenicity of quinone methides of 7-hydroxyflavylium salts for Salmonella typhimurium

Several synthetic 7-hydroxyflavylium salts related to apigeninidin, a natural 3-deoxyanthocyanidin, have been studied in the Ames mutagenicity test using strain TA1537 of Salmonella typhimurium. Under the neutral pH conditions of the test, these flavylium salts are deprotonated through ionization of the C7-OH (pK_a′ = 4.2–4.4) to form quinone methides. Only the quinone methides of 4-methyl-7-hydroxyflavylium chloride and 4′-methoxy-4-methyl-7-hydroxy-flavylium chloride showed mutagenicity. Responses of 4–8 times the background were observed at the higher doses (1000 μg/plate), both with and without metabolic activation. It was concluded that the induction of frameshift mutagenicity by this group of compounds is caused by those quinone methides that have non-ionic, stable polycyclic structures at neutral pH.     

Molecular recognition of anions by synthetic receptors

Over the past year, several significant developments have been made in the field of anion binding. The fundamental principles of molecular recognition are increasingly being better understood, and of particular interest are reports of several synthetic anion receptors able to perform their task in complex natural media. Additionally, macroscopic devices such as anion specific electrodes and membranes based on a molecular recognition approach are now being made.     

Repair mechanisms involved in muscle regeneration following partial excision of the rat gastrocnemius muscle

The sequential cytological events of the regeneration process, after partial excision of the gastrocnemius muscle in the rat, were followed by light and electron microscopy. During the first 2 days after injury leukocytes and macrophages infiltrate into the traumatized area. Myogenic regeneration is then characterized by mainly two repair mechanisms. Mononucleated cells, that populate the excised area, most probably fuse together to give rise to newly formed multinucleated myotubes that further develop to striated myofibers. Another mechanism involves the repair of injured muscle fibers by the possible fusion of mononucleated cells with their necrotic cut ends. Consequently, by addition of nuclei and new muscular material, sarcoplasmic outgrowths from the injured fibers are formed. It is concluded that mainly two repair mechanisms are involved in the regeneration process following partial excision of a muscle: addition of new muscle fibers in a process similar to that of embryonic myogenesis and also meristic growth from the injured fibers.     

Antagonism by theophylline of respiratory inhibition induced by adenosine

The effects on respiration of an analogue of adenosine, L-2-N6-(phenylisopropyl)adenosine (PIA), and of the methylxanthine, theophylline, were determined in 19 vagotomized glomectomized cats whose end-tidal PCO2 was kept constant by means of a servo-controlled ventilator. Integrated phrenic nerve activity was used to represent respiratory output. Our results show that PIA, whether given systemically or into the third cerebral ventricle, depressed respiration. Systemically administered theophylline stimulated respiration. Theophylline given intravenously, or into the third ventricle not only reversed the depressive effects of previously administered PIA but caused further increases of respiration above the control level. Prior systemic administration of theophylline blocked both respiratory and hypotensive effects of subsequently administered PIA. Effects of either agent on medullary extracellular fluid pH did not explain the results. We conclude that the adenosine analogue PIA, acts to inhibit neurons in the brain that are involved in the control of respiration and that its effects are blocked by theophylline. We suggest that adenosine acts as a tonic modulator of respiration and that theophylline stimulates breathing by competitive antagonism of adenosine at neuronal receptor sites.     

Circumsporozoite protein of Plasmodium berghei: gene cloning and identification of the immunodominant epitopes.

The gene encoding the circumsporozoite (CS) protein of the rodent malaria parasite Plasmodium berghei was cloned and characterized. A cDNA library made from P. berghei sporozoite RNA was screened with a monoclonal antibody for expression of CS protein epitopes. The resulting cDNA clone was used to isolate the CS protein gene from a lambda library containing parasite blood-stage DNA. The CS protein gene contains a central region encoding two types of tandemly repeated amino acid units, flanked by nonrepeated regions encoding amino- and carboxy-terminal signal and anchorlike sequences, respectively. One of the central repeated amino acid unit types contains the immunodominant epitopes.     

Immune deficiency in the X-linked lymphoproliferative syndrome. I. Epstein-Barr virus-specific defects

Eleven males with XLP were evaluated for EBV-specific antibodies during periods of 2 to 7 yr. Variable responses to EBV-specific antigens were found. All 11 patients had subnormal anti-EBNA titers, which probably reflected a T cell deficiency. The patients showed four different patterns in their anti-VCA response: 1) two boys who had experienced malignant lymphoma mounted no antibodies at all; 2) two patients showed intermittent anti-VCA titers; 3) four males had persistently elevated anti-VCA titers; and 4) three patients showed normal anti-VCA titers. ADCC against EBV-infected cells was abnormally low in six patients and was elevated in two patients given gamma-globulin. ADCC titers did not correlate with anti-VCA titers. However, most patients with XLP failed to effect regression of autologous EBV-infected lymphoblastoid cell lines, indicating a deficiency in long-lived T cell-mediated immunity to EBV.     

Nucleic acid relationships among Acholeplasma species.

3H-labeled Acholeplasma DNA probes were generated in vitro by the nick-translation method and used to determine the nucleotide sequence homology among the type strains of the eight currently recognized species of Acholeplasma. Very little nucleotide sequence homology (less than or equal to 18%) was found among the eight species, with heteroduplexes showing at least 12% or more mismatching as determined by thermal elution midpoints. The small amount of nucleotide sequence homology among the eight species indicates that these species are quite distinct and are not closely related to each other genomically.     

Structure of the spectrin-actin binding site of erythrocyte protein 4.1

The complete primary structure of the functional site of erythrocyte protein 4.1 involved in spectrin-actin associations has been determined. The sequence of this domain, which contains 67 amino acids and has a molecular mass of 8045 daltons, has been obtained by NH2-terminal sequence analysis of an 8-kDa chymotryptic peptide, three endoproteinase lysine C-cleaved peptides and two peptides obtained by Staphylococcus aureus protease V8 cleavage. All peptides including the 8-kDa domain peptide were purified by reverse-phase high performance liquid chromatography. Antibodies against two different synthetic peptides of the 8-kDa domain are able to inhibit the association between protein 4.1, spectrin, and F-actin, corroborating that the 8-kDa domain is responsible for the formation of a ternary complex. A computer search of the 8-kDa sequence with the National Biomedical Research Foundation database did not detect any significant homologies to known sequences. Protein 4.1 is not related to any known proteins and may represent a new protein superfamily.