bluuebunny/crossref_metadata_2025 huggingface dataset:
Inhibition of growth of a prolactin and growth hormone-secreting pituitary tumor in rats by D-tryptophan-6 analog of luteinizing hormone-releasing hormone.
Authors: Torres-Aleman I , Redding T W , Schally A V
Published: May 2006

The effect of long-term administration of analogs of luteinizing hormone-releasing hormone (LH-RH) and somatostatin on the growth of the growth hormone (GH)- and prolactin (PRL)-secreting rat pituitary GH3 tumor was investigated. Daily administration of [D-Trp6]LH-RH (50 micrograms/day), early after inoculation of the GH3 tumor, inhibited tumor growth by more than 90% as compared to controls. Similarly, in two experiments, a single once-a-month injection of long-acting [D-Trp6]LH-RH microcapsules (in a dose calculated to release about 25 micrograms/day for 30 days) inhibited the growth of GH3 pituitary tumor by more than 50% 6 or 13 wk after transplantation, when the tumors were fully developed. Serum GH and PRL levels also were reduced markedly by treatment with [D-Trp6]LH-RH. On the other hand, the administration of an antagonistic analog of LH-RH, N-Ac-[D-Phe(4Cl)1,2, D-Trp3, D-Arg6, D-Ala10]LH-RH, did not significantly reduce the growth of this tumor, and the treatment with two different analogs of somatostatin, cyclo(Pro-Phe-D-Trp-Lys-Thr-Phe) and D-Phe-Cys-Phe-D-Trp-Lys-Thr-Cys-Thr NH2, appeared to enhance it. These results are in agreement with previous findings of growth inhibition of 7315a pituitary tumors with different hormone-secreting characteristics by agonistic analogs of LH-RH. The collective data from experimental work with rat pituitary tumor models support the contention that the use of [D-Trp6]LH-RH might be considered for the treatment of some patients with pituitary tumors who failed to respond to conventional therapy.
The Markoff-Duffin-Schaeffer inequalities abstracted
Authors: Duffin R. J. , Karlovitz L. A.
Published: May 2006

The
k
th Markoff-Duffin-Schaeffer inequality provides a bound for the maximum, over the interval -1 ≤
x
≤ 1, of the
k
th derivative of a normalized polynomial of degree
n
. The bound is the corresponding maximum of the Chebyshev polynomial of degree
n
,
T
= cos(
n
cos
-1
x
). The requisite normalization is over the values of the polynomial at the
n
+ 1 points where
T
achieves its extremal values. The inequality is an equality only if the polynomial equals
T
or -
T
. The proof uses complex variable theory. This paper deals with a well-known generalization of polynomials—namely, functions satisfying some of the oscillation and approximation properties of ordinary polynomials. In particular, the generalized Chebyshev polynomial exhibits the extremal oscillations characteristic of the classical Chebyshev polynomial. It is shown that the direct analogs of the Markoff-Duffin-Schaeffer inequalities hold in this abstract setting and that they are included as a special case. Moreover, the proof is more elementary.
A fidelity assay using "dideoxy" DNA sequencing: a measurement of sequence dependence and frequency of forming 5-bromouracil X guanine base mispairs.
Authors: Lasken R S , Goodman M F
Published: May 2006

DNA replication fidelity has been assayed by using a modified DNA sequencing reaction. In one experimental approach, dideoxycytidine 5'-triphosphate (ddCTP) was used as a chain terminator during replication of M13 phage DNA by the large fragment of DNA polymerase I. The deoxyribonucleotide analogue BrdUTP was used to compete against ddCTP-induced chain terminations as an assay for B X G base mispairing (B represents bromodeoxyuridine when the analogue is present as a base pair or base mispair). By comparing BrdUTP to dCTP for competition against ddCTP, an average misincorporation frequency for BrdUMP of 0.2% was found. A similar average misincorporation frequency has been measured previously for the incorporation of radioactively labeled BrdUMP and dCMP into the synthetic template-primer poly-[d(G,T)] X oligo(dA). The advantage of the sequencing method is that an error frequency is determined for each template guanine in a defined DNA sequence, thus providing information on the effect of neighboring base sequences on fidelity. Misincorporation frequencies varied no more than 5-fold among 50 template guanines tested. The approach used here is not limited for use with nucleotide analogues but is generally applicable in determining misincorporation frequencies and sequence specificities for any deoxynucleoside triphosphate substrate. In a second experimental approach, base mispairing between bromouracil and guanine was demonstrated directly by using 5-bromodideoxyuridine 5'-triphosphate (BrddUTP). A comparison of chain terminations attributable to BrddUTP and to dideoxythymidine 5'-triphosphate (ddTTP) revealed that B X A and T X A base pairs formed at about the same rate, whereas B X G mispairs occurred 4-10 times more frequently than T X G. The elevation in the frequency of B X G over T X G mispairs is consistent with the mutagenic behavior of the base analogue.
Laminin binds specifically to sulfated glycolipids.
Authors: Roberts D D , Rao C N , Magnani J L , Spitalnik S L , Liotta L A , Ginsburg V
Published: May 2006

Previous studies of the agglutination of erythrocytes by the basement membrane glycoprotein laminin have suggested that laminin binds to gangliosides [Kennedy, D.W., Rohrbach, D.H., Martin, G.R., Momoi, T. & Yamada, K.M. (1983) J. Cell. Physiol. 114, 257-262]. Based on the following evidence, however, we find that laminin binds specifically to sulfatides, not gangliosides. Monogalactosyl sulfatides, purified from sheep erythrocytes with a yield of 4.3 mg/kg of packed cells, bound laminin with high affinity as did authentic bovine brain sulfatide (galactosylceramide-I3-sulfate). The binding activity of these lipids and of total erythrocyte lipids was stable to alkali and neuraminidase treatment but labile to dilute acid under conditions that destroy sulfatides but not gangliosides. Of various glycolipid and phospholipid standards tested, only sulfatides bound laminin with high affinity. Sulfatide binding and agglutinating activities of proteolytic fragments of laminin indicated that the globular end regions of the 200-kDa subunits are required for both activities. Thus, monogalactosylsulfatides, and possibly other more complex sulfated glycolipids, are probably involved in the agglutination of erythrocytes. These results also suggest a physiological function of sulfatides in cell adhesion. The agglutination of erythrocytes by fibronectin is also inhibited by gangliosides [Yamada, K.M., Kennedy, D.W., Grotendorst, G.R. & Momoi, T. (1981) J. Cell. Physiol. 109, 343-351]. Fibronectin, however, did not bind to sulfatides with high affinity but rather bound with low affinity to all anionic lipids tested, including phospholipids, gangliosides, and sulfatides.
An adenovirus vector system used to express polyoma virus tumor antigens.
Authors: Mansour S L , Grodzicker T , Tjian R
Published: May 2006

We have used a generalized adenovirus vector system to express the three polyoma tumor (T) antigen proteins under the control of the adenovirus major late promoter. One hybrid virus, Ad-PySVR498, expresses high levels of polyoma middle and small T antigens. A second hybrid virus, Ad-LTSVR545, which contains a cDNA copy of the polyoma A gene, overproduces large T antigen. The T antigens produced are indistinguishable from their authentic polyoma counterparts as determined by immunoprecipitation and partial cleavage by V8 protease. Analysis of polyoma mRNAs encoded by the recombinant viruses showed that they initiate from the adenovirus major late promoter and contain the tripartite leader at their 5' ends. Large T antigen isolated from Ad-LTSVR545-infected cells by immunoaffinity was shown to bind selectively to polyoma DNA sequences that contain the origin of viral DNA replication as well as the sites for transcription initiation.
Effects of fibrinogen-binding tetrapeptides on mechanical properties of fine fibrin clots.
Authors: Bale M D , Müller M F , Ferry J D
Published: May 2006

The tetrapeptides Gly-Pro-Arg-Pro and Gly-His-Arg-Pro, analogs of the amino termini of the alpha and beta chains of fibrin monomer, respectively, were introduced by diffusion into fine unligated fibrin clots. Gly-Pro-Arg-Pro decreased the shear modulus of elasticity progressively and at a concentration of 5.8 mM the clot was eventually liquefied. The decrease in elastic modulus was accompanied by enormously enhanced viscoelastic creep under shear stress and irrecoverable deformation after removal of stress. However, the differential compliance (or modulus) for clots containing the tetrapeptide remained constant during creep and creep recovery, so the structure rearranged under stress without any permanent damage. Ligation with factor XIIIa and calcium largely eliminated these effects. From these changes in mechanical properties, it appears that Gly-Pro-Arg-Pro competes for binding sites, with consequent depolymerization. The tetrapeptide Gly-His-Arg-Pro at comparable concentrations decreased the modulus and increased the creep to a lesser degree; when combined with Gly-Pro-Arg-Pro it enhanced the effectiveness of the latter.
Characterization of an HLA DR beta pseudogene.
Authors: Larhammar D , Servenius B , Rask L , Peterson P A
Published: May 2006

The class II molecules of the human major histocompatibility complex include the DR, DC, and SB antigens, each composed of an alpha and a beta polypeptide chain. We have isolated a DR beta gene in overlapping cosmid clones made from genomic DNA of a Dw4/DR4 homozygous individual. This gene consists of six exons and spans greater than 20 kilobases. Upon sequencing, it was found to possess several deleterious mutations, each capable of rendering the gene nonfunctional: (i) four splice junctions deviate from the G-T/A-G rule; (ii) two premature termination codons are present in the first domain exon; (iii) a 2-base-pair insertion causes a translational frame shift in the second domain exon. In addition, several amino acid residues that are conserved in all known expressed beta chains have been replaced in the amino acid sequence predicted from the pseudogene. Analysis of the pattern of nucleotide substitutions in the second domain exon suggests that most amino acid replacements occurred after the gene was inactivated. The inactivation may have been caused by insertion of a Kpn I repeat 5' to the promoter region, thereby interfering with transcription of the gene through removal of transcriptional enhancer elements. The DR beta pseudogene seems to be present also in other DR4 individuals.
Leukotriene B5 is formed in human neutrophils after dietary supplementation with icosapentaenoic acid.
Authors: Strasser T , Fischer S , Weber P C
Published: May 2006

Incorporation and conversion of icosapentaenoic acid (20:5, n - 3) by human polymorphonuclear leukocytes were studied in volunteers (n = 6) ingesting a normal Western diet supplemented with icosapentaenoic acid (approximately equal to 4 g daily). Ingestion of icosapentaenoic acid leads to formation of biologically less active leukotriene B5 (LTB5) from polymorphonuclear leukocytes (PMNL) stimulated with ionophore A23187. LTB5 was identified on HPLC by UV absorption and by GC/MS and showed a behavior identical to that of in vitro synthesized LTB5 produced by incubation of human PMNL with icosapentaenoic acid. The ratio of icosapentaenoic acid/arachidonic acid (20:4, n - 6) in cellular phospholipids increased from 0.045 during control to 0.28 after the supplemented period. LTB5 increased from undetectable values to 70.2 +/- 18.7 pmol of LTB5 per 10(7) PMNL during the experimental period. Synthesis of LTB4 did not change significantly (control, 218.8 +/- 89.1; icosapentaenoic acid-enriched diet, 253.6 +/- 18.7 pmol per 10(7) PMNL). The ratio of LTB4/LTB5 corresponded to the ratio of arachidonic acid/icosapentaenoic acid in PMNL phospholipids. Our findings prove that LTB5, which is 10 to 30 times less potent than LTB4 to cause aggregation, chemotaxis, and degranulation of PMNL, can be formed in vivo in man after dietary icosapentaenoic acid. This may modify the contribution of leukotrienes in processes in which these metabolites are of pathogenetic relevance.
Influenza A virus nucleoprotein is a major target antigen for cross-reactive anti-influenza A virus cytotoxic T lymphocytes.
Authors: Yewdell J W , Bennink J R , Smith G L , Moss B
Published: May 2006

Influenza A virus-specific cytotoxic T lymphocytes (CTL) capable of lysing cells infected with any influenza A virus ("cross-reactive CTL") constitute a major portion of the host CTL response to influenza. The viral nucleoprotein (NP), a major internal virion structural protein, has been implicated as a possible target antigen for cross-reactive CTL. To directly examine CTL recognition of NP, a vaccinia virus recombinant containing a DNA copy of an influenza A virus NP gene was constructed. We found that murine cells infected with this virus were efficiently lysed in a major histocompatibility complex-restricted manner by cross-reactive CTL populations obtained by immunization with a variety of influenza A virus subtypes. In addition, the recombinant vaccinia virus containing the PR8 NP gene was able to both stimulate and prime for a vigorous secondary cross-reactive CTL response. Significantly, splenocytes from mice primed by inoculation with the recombinant vaccinia virus containing the PR8 NP gene could be stimulated by influenza A viruses of all three major human subtypes. Finally, unlabeled target competition experiments suggest that NP is a major, but not the sole, viral target antigen recognized by cross-reactive CTL.
Fracture dynamics of fusion of two anti-plane cracks
Authors: Chatterjee A. K. , Knopoff L.
Published: May 2006

The problem of the fracture dynamics of two two-dimensional coplanar anti-plane shear cracks is considered. Both cracks extend under a critical stress-intensity fracture criterion. The two cracks are initiated at different locations and times. A solution developed by Kostrov [Kostrov, B. V. (1966)
J. Appl. Math. Mech.
30, 1241-1248] for isolated cracks is used to determine the tearing loci of the cracks up to the time at which the individual cracks begin to interact. In the interaction interval prior to the fusion of the two cracks, both the stresses and the fracture tip loci are determined sequentially by applying the solution to Abel's equation twice iteratively. This method can be used to solve problems of the fusion of any number of coplanar cracks.
Total synthesis of (+/-)-11 alpha-hydroxyprogesterone by cyclization of a polyunsaturated epoxide.
Authors: van Tamelen E E , Faler D L
Published: May 2006

The total synthesis of a typical 11-hydroxylated steroid, (+/-)-11 alpha-hydroxyprogesterone, was achieved by picric acid-catalyzed tricyclization of a polyunsaturated epoxide appropriately substituted with ketal, hydroxyl, and acetylenic units. This epoxide was prepared by a multistage sequence featuring two successive alkylations of intermediary, monocyclic sulfones. The first sulfone intermediate was obtained by means of a short sequence starting from levulinic acid and diethyl succinate and involving a selective cyclization reaction.
Characterization of a yeast mitochondrial promoter by deletion mutagenesis.
Authors: Biswas T K , Edwards J C , Rabinowitz M , Getz G S
Published: May 2006

We have generated collections of mutants of the promoter for the small rRNA gene from the mitochondria of yeast deleted from either the 3' or 5' end. Plasmids containing the partially deleted promoter were assayed for their ability to direct correct transcriptional initiation in a homologous in vitro system. We find that the region required for high-efficiency promoter function lies between positions -10 and +2. Our methods detected no effect of flanking sequences on the strength of this promoter.
Brain-specific polypeptide 1B236 exists in multiple molecular forms.
Authors: Malfroy B , Bakhit C , Bloom F E , Sutcliffe J G , Milner R J
Published: May 2006

The COOH-terminal amino acid sequence of the rat brain-specific polypeptide 1B236 was previously deduced from molecular cloning and nucleotide sequence determination of its mRNA and the 1B236 protein shown to exist in the rat brain. The amino acid sequence of 1B236 contained at least three peptide sequences demarcated by pairs of basic amino acids--a structure similar to known neuropeptide and hormone precursors--which suggested that the protein might be processed in vivo to generate peptides. We have developed radioimmunoassays specific for 1B236 with antibodies against three synthetic peptides corresponding to putative cleavage products of this protein and have used these assays to define the molecular forms of 1B236 in rat brain extracts. The most abundant form is of high molecular weight (ca. 100,000) and requires detergent for solubilization; hence, it is probably membrane-bound. However, a small fraction of the high molecular weight material is soluble in the absence of detergent. In addition, several low molecular weight species are detectable in brain extracts prepared under conditions preventing proteolysis. These molecules correspond in size to two of the possible products of proteolytic processing predicted from the amino acid sequence of 1B236. The multiplicity of 1B236 forms, together with other data, suggests that this protein undergoes extensive post-translational modification, including proteolytic processing to generate peptides that may be physiologically relevant.
Possible involvement of human D minigenes in the first complementarity-determining region of kappa light chains.
Authors: Chen P P , Kabat E A , Wu T T , Fong S , Carson D A
Published: May 2006

The nucleotide sequences of the complementary strands of two human diversity region (D) minigenes, D2 and D4, show stretches of homology with two human variable region kappa chain (V kappa) genes, NG9 and HK101, respectively, in the first complementarity-determining region. In one V kappa sequence, the homology includes the 5' flanking region of D minigenes, which may comprise a recombinase recognition signal. It is thus conceivable that gene conversions involving D minigenes may contribute to V kappa diversity.
Harmonic maps of S
2
into a complex Grassmann manifold
Authors: Chern Shing-Shen , Wolfson Jon
Published: May 2006

Let G(
k
,
n
) be the Grassmann manifold of all C

k

in C

n

, the complex spaces of dimensions
k
and
n
, respectively, or, what is the same, the manifold of all projective spaces P

k
-1

in P

n
-1

, so that G(1,
n
) is the complex projective space P

n
-1

itself. We study harmonic maps of the two-dimensional sphere S
2
into G(
k
,
n
). The case
k
= 1 has been the subject of investigation by several authors [see, for example, Din, A. M. & Zakrzewski, W. J. (1980)
Nucl. Phys. B
174, 397-406; Eells, J. & Wood, J. C. (1983)
Adv. Math.
49, 217-263; and Wolfson, J. G.
Trans. Am. Math. Soc.,
in press]. The harmonic maps S
2
→ G(2, 4) have been studied by Ramanathan [Ramanathan, J. (1984)
J. Differ. Geom.
19, 207-219]. We shall describe all harmonic maps S
2
→ G(2,
n
). The method is based on several geometrical constructions, which lead from a given harmonic map to new harmonic maps, in which the image projective spaces are related by “fundamental collineations.” The key result is the degeneracy of some fundamental collineations, which is a global consequence, following from the fact that the domain manifold is S
2
. The method extends to G(
k
,
n
).
Molecular cloning, cDNA sequencing, and chemical synthesis of cecropin B from Hyalophora cecropia.
Authors: van Hofsten P , Faye I , Kockum K , Lee J Y , Xanthopoulos K G , Boman I A , Boman H G , Engström A , Andreu D , Merrifield R B
Published: May 2006

Two cDNA clones containing coding information for cecropin B from the Cecropia moth (Hyalophora cecropia) were identified by means of a synthetic probe. Sequencing of the two inserts showed that cecropin B is processed from a 62-amino acid residue precursor molecule including a 26-residue leader peptide and a COOH-terminal glycine residue. The latter presumably donates the nitrogen of the amide group present on the COOH-terminal leucine residue of the mature cecropin B. The sequence deduced for the mature cecropin B differed in the COOH-terminal region from the tentative structure previously determined by carboxypeptidase digestion. To settle the discrepancy, cecropin B was synthesized according to the cDNA sequence with an amidated COOH-terminal leucine. Natural and synthetic cecropin B were found to be indistinguishable with respect to electrophoretic mobility and antibacterial activity against seven different bacteria. The COOH-terminal tetrapeptides were isolated from both natural and synthetic cecropin B and found to be indistinguishable. The correct sequence for cecropin B is (formula; see text).
Site-specifically modified oligodeoxyribonucleotides as templates for Escherichia coli DNA polymerase I.
Authors: O'Connor D , Stöhrer G
Published: May 2006

Oligodeoxyribonucleotides with site-specific modifications have been used as substrates for Escherichia coli DNA polymerase I holoenzyme and Klenow fragment. Modifications included the bulky guanine-8-aminofluorene adduct and a guanine oxidation product resembling the product of photosensitized DNA oxidation. By a combination of primers and "nick-mers", conditions of single-strand-directed DNA synthesis and nick-translation could be created. Our results show that the polymerase can bypass both types of lesions. Bypass occurs on a single-stranded template but is facilitated on a nicked, double-stranded template. Only purines, with guanine more favored than adenine, are incorporated across both lesions. Hesitation during bypass could not be detected. The results indicate that site-specifically modified oligonucleotides can be sensitive probes for the action of polymerases on damaged templates. They also suggest a function for polymerase I, in its nick-translation capacity, during DNA repair and mutagenesis.
Growth-dependent expression of multiple species of DNA methyltransferase in murine erythroleukemia cells.
Authors: Bestor T H , Ingram V M
Published: May 2006

Friend murine erythroleukemia cells were found to contain three distinct species of DNA (cytosine-5-)-methyltransferase (DNA MeTase) whose relative proportions were a characteristic function of the proliferative state of the cells. Rapidly proliferating cells contained a Mr 190,000 species of DNA MeTase (DNA MeTase III), whereas cells in the late logarithmic/early plateau phase of cellular growth contained two species of Mr 150,000 and 175,000 (DNA MeTase I and II); stationary phase cells contained primarily DNA MeTase I. The three species of DNA MeTase displayed structural similarities, as determined by analysis of partial proteolysis products, and have similar de novo sequence specificities in transmethylation reactions involving purified enzyme and prokaryotic DNA. The different relative proportions of the enzymes in cells under different growth conditions suggest that the three species of DNA MeTase fulfill different roles in processes leading to the perpetuation of DNA methylation patterns.
Active site and complete sequence of the suicidal methyltransferase that counters alkylation mutagenesis.
Authors: Demple B , Sedgwick B , Robins P , Totty N , Waterfield M D , Lindahl T
Published: May 2006

The inducible resistance to alkylation mutagenesis and killing in Escherichia coli (the adaptive response) is controlled by the ada gene. The Ada protein acts both as a positive regulator of the response and as a DNA repair enzyme, correcting premutagenic O6-alkylguanine in DNA by suicidal transfer of the alkyl group to one of its own cysteine residues. We have determined the DNA sequence of the cloned ada+ gene and its regulatory region. The data reveal potential sites of ada autoregulation. Amino acid sequence determinations show that the active center for the O6-methylguanine-DNA methyltransferase is located close to the polypeptide COOH terminus and has the unusual sequence -Pro-Cys-His-, preceded by a very hydrophobic region. These same structural features are present at the active site of thymidylate synthase, suggesting a common chemical mechanism for activation of the cysteine.
5-Azacytidine and sodium butyrate induce expression of aromatase in fibroblasts from chickens carrying the henny feathering trait but not from wild-type chickens.
Authors: Leshin M
Published: May 2006

Male chickens with the henny feathering trait have a female feathering pattern. In two henny-feathered breeds, the Sebright bantam and the Golden Campine, the synthesis of estrogen is increased as a consequence of increased activity of aromatase, a cytochrome P-450 enzyme that converts androgen to estrogen. The activity of the enzyme is elevated in tissue slices and in cultured fibroblasts from heterozygous and homozygous birds of both breeds. In contrast, aromatase activity is very low in extraglandular tissues from control chickens and is undetectable in fibroblasts cultured from these tissues. The current studies show that two agents known to alter gene expression--5-azacytidine and sodium butyrate--markedly induce expression of aromatase activity in Sebright and Campine fibroblasts but have no effect on aromatase activity in fibroblasts from wild-type chickens. Induction of aromatase is specific since two other microsomal enzymes in chicken fibroblasts--one, a component of the aromatase enzyme complex and the other a cytochrome P-450 oxidase distinct from the aromatase--are not significantly affected by these agents. Further study of this unique mutation should provide insight into the mechanisms by which genes are switched to an uninducible state during differentiation.
Continuous Stern-Gerlach effect: Noise and the measurement process
Authors: Dehmelt Hans
Published: May 2006

This paper resumes the discussion of the continuous Stern-Gerlach effect, a method to continuously and nondestructively determine the spin state of the same individual electron, quasipermanently confined in a Penning trap in ultrahigh vacuum at liquid helium temperatures. Here the focus is on limitations to spin-state detection due to thermal and zero-point noise and on the quantum-mechanical measurement process. Illustrations of the continuous spin measurement process in the presence of selected perturbations are provided. The alteration of the spin state brought about by the frequency measurement process is exhibited. To resolve Zeno's paradox in a specific example, a slow resonant spin flip is discussed, when interrupted by frequent spin-state measurements. The continuous Stern-Gerlach effect is shown to be a near-ideal example for the quantum mechanical measurement process, for which all steps may be followed in quantitative detail.
Stable accumulation of a rat truncated repeat transcript in Xenopus oocytes.
Authors: Gutierrez-Hartmann A , Baxter J D
Published: May 2006

To define potential mechanisms of expression of middle-repetitive DNA, Xenopus oocytes were employed to examine the rat type 2 and truncated repeat (TR) elements contained in an intron and in the 3'-flanking region of the rat growth hormone gene. These repeats contain significant sequence and structural homology to tRNA genes and, thus, may represent tRNA pseudogenes. Transcripts from the type 2 elements do not accumulate in the cytosol and are found predominantly in the nucleus, whereas those from TR DNA are expressed in the cytosol of neural and pituitary tissues. In HeLa cell extracts, the rat growth hormone type 2 sequences initiate RNA polymerase III transcription resulting in multiple transcripts of 175-970 nucleotides; some of these also contain TR sequences that are present only as downstream structures since the rat growth hormone-TR DNA lacks promoter activity. In Xenopus oocytes the same template also results in multiple transcripts, but with time a single, homogeneous 73-base RNA preferentially accumulates. This RNA probably arises from larger repetitive DNA transcripts as assessed by the kinetics of its formation, its 5' terminus, and the injection of transcripts generated in HeLa cell-free extracts into the oocytes. Sequence analysis of the 73-base RNA suggests that it is a TR transcripts derived from the TR region with tRNA homology. Stable type 2 transcripts were not detected. Thus, type 2 elements are transcribed in the oocytes, but RNAs from them are degraded whereas discrete TR DNA transcripts can be derived from larger RNA molecules and can accumulate in the cytosol due to their preferential stability. These findings indicate that posttranscriptional control mechanisms can operate to direct differential expression of closely related repetitive DNAs and suggest that structures similar to tRNA contained within the TR sequences may allow them to accumulate preferentially in the cytoplasm.
The qa repressor gene of Neurospora crassa: wild-type and mutant nucleotide sequences.
Authors: Huiet L , Giles N H
Published: May 2006

The qa-1S gene, one of two regulatory genes in the qa gene cluster of Neurospora crassa, encodes the qa repressor. The qa-1S gene together with the qa-1F gene, which encodes the qa activator protein, control the expression of all seven qa genes, including those encoding the inducible enzymes responsible for the utilization of quinic acid as a carbon source. The nucleotide sequence of the qa-1S gene and its flanking regions has been determined. The deduced coding sequence for the qa-1S protein encodes 918 amino acids with a calculated molecular weight of 100,650 and is interrupted by a single 66-base-pair intervening sequence. Both constitutive and noninducible mutants occur in the qa-1S gene and two different mutations of each type have been cloned and sequenced. All four mutations occur within the predicted coding region of the qa-1S gene. This result strongly supports the hypothesis that the qa-1S gene encodes a repressor. All four mutations are located within codons for the last 300 amino acids of the qa-1S protein. The mutations in three of the mutants involve amino acid substitutions, while the fourth mutant, which has a constitutive phenotype, contains a frameshift mutation. The two constitutive mutations occur in the most distal region of the gene, possibly implicating the COOH-terminal region of the qa repressor in binding to its target. The two noninducible mutations occur in a region proximal to the constitutive mutations, possibly implicating this region of the qa repressor in binding the inducer.
Suppression of lymphocyte activation and functions by a leukemia cell-derived inhibitor.
Authors: Chiao J W , Heil M , Arlin Z , Lutton J D , Choi Y S , Leung K
Published: May 2006

An inhibitor isolated from the serum-free culture medium of human myeloid leukemic HL-60 cells was able to suppress mitogen- and alloantigen-stimulated proliferative responses of normal lymphocytes in a dose-dependent manner. In vitro production, concentration, and purification by column chromatography and electrophoresis revealed that the inhibitor was produced constitutively, required RNA synthesis, and had a molecular weight in the range of 40,000-60,000. The inhibitor was also produced in vitro by myeloid leukemia cells isolated from patients with acute myelogenous leukemia. In a similar manner, the inhibitory material suppressed proliferative responses of allogeneic and autologous lymphocytes. Suppression was accompanied by drastically reduced production of interleukin 2 and lymphokines, which regulate differentiation of myeloid leukemia cells, and suppression was reversed by addition of exogenous interleukin 2. The inhibitor did not suppress clonogenic proliferation of normal granulocytes and macrophages suggesting that inhibition of production or interference with interleukin 2 activity as a possible mechanism. These interactions between leukemia cells and lymphocytes have shed new light on the immunosuppression and growth advantage of leukemia cells. Inhibitory activity of HL-60 cells was diminished after they were induced to differentiate, indicating that differentiation induced by lymphokines may be an effective means of controlling leukemia.
Effect of atrial natriuretic peptide on gonadotropin release in superfused rat pituitary cells.
Authors: Horvath J , Ertl T , Schally A V
Published: May 2006

Cardiac atrial muscle cells produce a polypeptide hormone that plays a role in the control of water and electrolyte balance and blood pressure. The circulating form of this hormone is the atrial natriuretic peptide (ANP), which contains 28 amino acids. Various immunohistochemical studies have shown that ANP is present in many areas of the central nervous system, including the median eminence. In our studies, we investigated the effect of ANP in a superfused rat pituitary cell system. When ANP was administered at increasing concentrations (0.01 microM to 1 microM), it caused a significant dose-related stimulation of the release of luteinizing hormone (LH) and follicle-stimulating hormone (FSH). The lowest effective dose of ANP in our system was 0.03 microM. When ANP and LH-releasing hormone were administered together, the response was prolonged and had the characteristics of ANP-stimulated LH and FSH release. In contrast with some previous reports, ANP in high concentration (1 microM) consistently induced a small but significant stimulation of the release of corticotropin. ANP did not influence the basal release of prolactin, growth hormone, and thyrotropin.
Identification of proteins that bind tightly to pre-mRNA during in vitro splicing.
Authors: Mayrand S H , Pedersen N , Pederson T
Published: May 2006

Incubation of a human beta-globin pre-mRNA in a HeLa cell nuclear extract under conditions permissive for efficient splicing resulted in the assembly of the RNA into ribonucleoprotein (RNP) complexes. This RNP formation occurred largely within the characteristic lag period that precedes splicing. Two classes of RNP were detected by the criterion of their stability in Cs2SO4 gradients. One was unstable and contained mainly aberrant RNA cleavage products. The other class of RNP complexes comprised 50-85% of the beta-globin RNA, formed only under splicing-permissive conditions, was stable in Cs2SO4 gradients, and contained both unspliced pre-mRNA molecules and the lariat intron 1-exon 2 splicing intermediate. This latter class of RNP complexes banded at approximately equal to 1.30 g/cm3, a density very similar to that of native heterogeneous nuclear RNP particles that contain pre-mRNA. RNA-protein crosslinking revealed major proteins of Mr approximately equal to 38,000 and 41,000 in the stable class of RNP. The use of antibodies specific for heterogeneous nuclear RNP core proteins and for small nuclear RNA-associated proteins, in conjunction with [32P]RNA-protein crosslinking, revealed polypeptides having the molecular weights of both sets of antigens. These results show that both heterogeneous nuclear RNP particle core proteins and small nuclear RNA-associated proteins bind tightly to pre-mRNA during splicing in vitro.
Platelet-derived growth factor modulates epidermal growth factor receptors by a mechanism distinct from that of phorbol esters.
Authors: Olashaw N E , O'Keefe E J , Pledger W J
Published: May 2006

Platelet-derived growth factor (PDGF) and phorbol 12-myristate 13-acetate (PMA) decrease high affinity binding of 125I-labeled epidermal growth factor (EGF) and potentiate mitogenesis in BALB/c 3T3 cells, and both have been shown to induce the phosphorylation of the EGF receptor at threonine residues. These similarities suggest that the actions of PDGF on EGF binding may be mediated by protein kinase C, the cellular effector of PMA. We show that in density-arrested BALB/c 3T3 cells PDGF and PMA induce a rapid, transient, cycloheximide-independent loss of EGF binding activity. As has been previously shown for PDGF, the ability of PMA to reduce EGF binding was enhanced by cholera toxin, a potent activator of adenylate cyclase. In contrast to PMA, however, PDGF induced a further reduction in EGF binding that was strictly dependent upon continued protein synthesis. Furthermore, PDGF effectively reduced EGF binding in cells refractory to PMA. Cells desensitized to PMA, presumably due to the loss of protein kinase C activity, also remained mitogenically responsive to PDGF. These data suggest that the mechanism by which PDGF modulates EGF binding differs from that of PMA and thus, at least in part, is independent of protein kinase C.
Rearrangement mutations on the 5' side of the qa-2 gene of Neurospora implicate two regions of qa-1F activator-protein interaction.
Authors: Geever R F , Murayama T , Case M E , Giles N H
Published: May 2006

Transcriptional activation of the Neurospora crassa qa genes normally requires the positive regulatory gene, qa-1F+, whose function is controlled by the inducer quinic acid and by the product of the negative regulatory gene, qa-1S+. The properties of qa-1F+ activator have been examined in transcriptional mutations of the qa-2 structural gene, in which activator-independent transcription of qa-2 (qa-2ai mutants) occurs in strains having a qa-1F- gene. Seven qa-2ai mutants with DNA rearrangements in different 5' regions of qa-2 were analyzed in qa-1F+ strains. In five with rearrangements at position -190 or further upstream, expression of the qa-2 gene was inducible, and induction was accompanied by a change in the initiation site for transcription from position -45, characteristic of constitutive initiation in qa-2ai mutants to position +1, characteristic of the induced wild type. In two mutants with breakpoints at positions -86 and -53, qa-2 transcription initiated from upstream sequences within the rearrangements but not at the +1 site, and qa-2 expression was noninducible. The results indicate that (i) sequences between positions -190 and -86 are required for positive control of initiation at position +1, and (ii) negative control does not require sequences downstream of position -86. Additional evidence suggests that the product of the qa-1F+ gene in the noninduced state may also interact with distal upstream sequences positioned midway between divergently transcribed qa genes.
Gonadotropin-releasing hormone differentially regulates expression of the genes for luteinizing hormone alpha and beta subunits in male rats.
Authors: Papavasiliou S S , Zmeili S , Khoury S , Landefeld T D , Chin W W , Marshall J C
Published: May 2006

Gonadotropin-releasing hormone (GnRH) and gonadal steroids regulate synthesis and release of luteinizing hormone (LH). GnRH is secreted intermittently by the hypothalamus, producing pulsatile LH release, and a pulsatile GnRH stimulus is required to maintain LH secretion. We report the regulatory effects of GnRH pulse injections on pituitary concentrations of LH alpha and beta subunit mRNAs in a castrated/testosterone-replaced male rat model. Replacement with physiologic amounts of testosterone decreased concentrations of both LH subunit mRNAs. GnRH pulse injections (10-250 ng per pulse given every 30 min for 48 hr) increased both mRNA concentrations, but the dose response patterns were markedly different. alpha subunit mRNA was increased by all GnRH doses but not the levels seen after castration alone. In contrast, LH beta subunit mRNA concentrations showed a marked dependence on GnRH dose. Maximal responses, to values similar to those in castrates, occurred after 25-ng GnRH pulses, and larger doses produced a smaller increase in LH beta subunit mRNA. Both the acute LH secretory response to GnRH and the number of GnRH receptors followed a pattern similar to the LH beta subunit mRNA concentration and were maximal after the 25-ng GnRH dose. These results show that GnRH can differentially regulate LH subunit mRNAs and suggest that concentrations of LH beta subunit mRNA may be a limiting factor in GnRH-stimulated LH release.
A naturally occurring deletion in the mouse Hbbs beta-globin gene cluster.
Authors: Holdener-Kenny B , Weaver S
Published: May 2006

A restriction fragment size difference of 1.9 kilobases exists between the C57BL/10 (Hbbs) and BALB/c (Hbbd) beta-globin gene clusters in the vicinity of the Hbb-y and Hbb-bh0 genes. This length difference is the result of a deletion that removes the majority of the C57BL/10 Hbb-bh0 gene. The Hbb-bh0 deletion appears to be widespread among Hbbs-carrying mice. In addition to the deletion, 119 base pairs of DNA of unknown origin are found in C57BL/10 DNA at the point of discontinuity. The existence of this deletion is inconsistent with reports of transcripts homologous to the third exon of the Hbb-bh0 gene in both C57BL/10 embryos and in a cell line carrying the Hbbs haplotype. We propose that the Hbb-bh0 gene is a recently disabled pseudogene.
Detection and sequence of plus-strand leader RNA of sonchus yellow net virus, a plant rhabdovirus
Authors: Zuidema Douwe , Heaton Louis A. , Hanau Robert , Jackson A. O.
Published: May 2006

Tobacco infected with the plant rhabdovirus sonchus yellow net virus (SYNV) contains short, 139- to 144-nucleotide (nt) transcripts complementary to the 3′ terminus of the negative-strand genomic RNA. These transcripts are similar to the leader RNAs associated with several animal rhabdovirus infections in that they are encoded by the same region of the genome, but the SYNV transcripts are nearly 3 times longer than the animal rhabdovirus leader RNAs. The SYNV leader RNAs differ markedly in sequence from the leader RNAs associated with strains of vesicular stomatitis virus and rabies virus, although the first 30 nt of all three transcripts are rich in adenylate residues. The nucleotide sequence determined directly from SYNV RNA and from recombinant DNA clones derived from SYNV RNA reveals a possible initiation site for transcription of the N-protein mRNA that is located 147 nt from the 3′ end of genomic RNA. The sequence (UUGU) at this site is complementary to the first 4 nt of the N-protein mRNAs of animal rhabdoviruses. In SYNV, the first AUG codon in the putative N-protein mRNA is located 57 nt downstream (at positions 203-205 in the viral genome) and is followed by an open reading frame for the remainder of the 1020 nt determined in these experiments.
Cell cycle-specific replication of Escherichia coli minichromosomes.
Authors: Leonard A C , Helmstetter C E
Published: May 2006

The timing of Escherichia coli minichromosome replication in the cell division cycle was examined using an improved procedure for studying plasmid replication frequency. Cultures growing exponentially in glucose/Casamino acids minimal medium were pulse-labeled with [3H]thymidine, and the radioactivity incorporated into plasmid DNA in cells of different ages was analyzed. At the end of the labeling period the bacteria were bound to the surface of a nitrocellulose membrane filter, and the radioactivity in new daughter cells, which eluted continuously from the membrane, was quantitated following agarose gel electrophoresis. The minichromosomes replicated during a discrete interval in the cell division cycle that appeared to coincide with initiation of chromosome replication. In contrast, plasmid pBR322 replicated throughout the division cycle at a rate that increased gradually as a function of cell age. The difference in minichromosome and pBR322 replication was clearly discernible in cells harboring both plasmids. It was also found that the 16 kD gene adjacent to oriC was not a determinant of the timing of minichromosome replication during the division cycle. The results are consistent with the conclusion that minichromosome replication frequency is governed by the same mechanism that controls chromosome replication.
Expression of the protein encoded by the 3' open reading frame of human T-cell lymphotropic virus type III in bacteria: demonstration of its immunoreactivity with human sera.
Authors: Franchini G , Robert-Guroff M , Wong-Staal F , Ghrayeb J , Kato I , Chang T W , Chang N T
Published: May 2006

The genome of human T-cell lymphotropic virus type III/lymphadenopathy-associated virus (HTLV-III/LAV), the infectious agent etiologically associated with the acquired immunodeficiency syndrome, contains, in addition to the genes for the polymerase, core, and envelope proteins, several open reading frames. To investigate whether the 3' open reading frame (3' orf) located between the envelope gene and the 3' long terminal repeat is a gene expressed in vivo in infected individuals, we inserted a fragment of 3' orf in a prokaryotic expression vector. The protein product synthesized in bacteria was purified and allowed to react with sera from individuals infected with human T-cell lymphotropic virus type III as indicated by seropositivity for other viral proteins. Two-thirds of the sera, regardless of the clinical status of the individuals, reacted with the purified protein indicating that 3' orf is a viral gene the product of which is immunogenic in vivo. A polyclonal rabbit antiserum reacting against the 3' orf gene product was obtained by serial injection of rabbits with the purified bacterial protein. The antiserum recognized a 27-kDa protein in the human T-cell lymphotropic virus type III-infected lymphocytes.
Discrete wave mechanics: The hydrogen atom
Authors: Wall Frederick T.
Published: May 2006

The quantum mechanical problem of the hydrogen atom is treated by use of a finite difference equation in place of Schrödinger's differential equation. The exact solution leads to a wave vector energy expression that is readily converted to the Bohr-Rydberg formula. (The calculations here reported are limited to spherically symmetric states.) The wave vectors reduce to the familiar solutions of Schrödinger's equation as
c
→ ∞. The internal consistency and limiting behavior provide support for the view that the equations employed could well constitute an approach to a relativistic formulation of wave mechanics.
In vitro reconstitution of flagellar filaments onto hooks of filamentless mutants of Salmonella typhimurium by addition of hook-associated proteins.
Authors: Homma M , Iino T , Kutsukake K , Yamaguchi S
Published: May 2006

An in vitro system for reconstituting flagellar filaments onto hooks of filamentless mutants of Salmonella typhimurium was used to investigate the role played in filament formation by the three hook-associated proteins (HAPs, products of the flaW, flaU, and flaV genes). These proteins--FlaW, FlaU, and FlaV--are believed to be assembled in this order at the distal end of the hook. When the recipient hooks were provided by flaU mutants, whose hook tips contained FlaW only, exogenous FlaU was essential for polymerization of both exogenous and endogenous flagellin, whereas exogenous FlaV inhibited such polymerization. When the recipients were flaV-mutant hooks, whose tips contained FlaW and FlaU but not FlaV, exogenous FlaV inhibited polymerization of exogenous flagellin. FlaV also inhibited polymerization of exogenous flagellin at the tips of filament fragments. In contrast, FlaV was essential for polymerization of endogenous flagellin onto flaV-mutant hooks, and onto short filaments that had been made (in the absence of FlaV) by polymerization of exogenous flagellin on the tips of flaV-mutant hooks. These results suggest that FlaV acts not only at the tip of the hook to initiate growth of the filament, but also at the tip of the growing filament, and that FlaV is essential for polymerization of endogenous flagellin--i.e., for the normal process of filament assembly in vivo.