bluuebunny/crossref_metadata_2025 huggingface dataset:
Differences in Fe(II)-N epsilon(His-F8) stretching frequencies between deoxyhemoglobins in the two alternative quaternary structures.
Authors: Nagai K , Kitagawa T
Published: May 2006

Resonance Raman spectra have been obtained of the alpha deoxy and beta deoxy subunits within valency hybrid hemoglobins both in the high-affinity (R) and low-affinity (T) structures. Upon conversion from the R to the T structure, the vibrational frequency of the Fe(II)-N epsilon(His-F8) bond changes from 223 to 207 or 203 cm-1 in the alpha deoxy subunit and from 224 to 220 or 217 cm-1 in the beta deoxy subunit. We estimate that the Fe(II)-N epsilon(His-F8) bond is stretched by the R leads to T transition 3 times more in the alpha subunit (0.024 A) than in the beta subunit (0.0085 A) and, accordingly, the strain energy developed in that bond is 8 times larger in the alpha than in the beta subunit. Hence, the oxygen affinity of the alpha and beta subunits may be regulated by different mechanisms.
Kinetics of erythroid precursors in mice infected with the anemic or the polycythemic strain of Friend leukemia virus
Authors: Peschle C. , Migliaccio G. , Lettieri F. , Migliaccio A. R. , Ceccarelli R. , Barba P. , Titti F. , Rossi G. B.
Published: May 2006

The kinetics of both erythroid burst-forming and colony-forming units (BFU-E, CFU-E) and myelomonocytic precursors [myelomacrophage colony-forming unit (CFU-C)] have been evaluated in tibial marrow, peripheral blood, and spleen of DBA/2 mice at time intervals after inoculation of either the anemic (FLV-A) or the polycythemic (FLV-P) strain of Friend leukemia virus. Either one of the viruses induced, at 7-10 days after infection, a massive increase in the number of BFU-Es in peripheral blood, in parallel with their depletion in tibial marrow and increase in spleen. A comparable increase in the blood BFU-E number was observed in splenectomized FLV-infected mice. These results indicate a marrow-spleen migration of BFU-Es. In spleen, the increase of the BFU-E number was associated with an increase in the CFU-E pool. In tibial marrow, a sequence of expansion/depletion waves occurred reciprocally at the level of BFU-E and CFU-E. The cycling of BFU-E([
3
H]thymidine
in vitro
suicide index) in marrow, blood, and spleen was enhanced, whereas that of CFU-E and CFU-C showed little or no modification. These kinetic data suggest that the main target cell of FLV may be the BFU-E or a closely related element. In plates without added erythropoietin (but containing it in fetal calf serum), expression of CFU-E from FLV-P-treated animals was maximal; that of CFU-E from FLV-A-injected mice was either virtually absent or only slight in marrow or spleen, respectively. BFU-E growth always was fully dependent upon erythropoietin addition. Control studies in FLV-infected resistant mice and in susceptible mice given diluted or heat-inactivated virus provide convincing evidence that the phenomena described are induced by FLV.
Control of growth of estrogen-sensitive cells: role for alpha-fetoprotein.
Authors: Soto A M , Sonnenschein C
Published: May 2006

The role played by alpha-fetoprotein (AFP) during the perinatal period in rats has not yet been ascertained despite earlier suggestions that this plasma protein affected the multiplication, in an "in animal-in culture" system of tumor cells that are stimulated by estrogen (E) for growth. To test this inference developed from our previous work, AFP was purified by reverse affinity chromatography to homogeneity by electrophoretic and immunochemical criteria. Purified AFP was added at different concentrations to horse serum-supplemented medium which by itself is able to allow maximal exponential growth of a rat pituitary tumor cloned cell line C29RAP. These cells carry estrophilins and their growth is stimulated by E in animals but not in culture. At 3 mg/ml in culture media, AFP prevented growth of C29RAP cells; the effect was dose dependent. F4C1, a rat pituitary cloned cell line that carries estrophilins but shows autonomous behavior when injected into male and female Fisher rats, was not affected in cultured by comparable concentrations of AFP in the culture media. The effect of AFP on the growth of E-sensitive cells in culture was not reversed by E administration. We conclude from these experiments that (i) AFP is a specific inhibitor of the cell multiplication of cells that are E-sensitive for growth (as defined in this presentation), (ii) estrophilins seem not to play a significant role in this inhibition, and (iii) E appears not to be a growth-promoting hormone per se.
Sustained growth in primary culture of normal mammary epithelial cells embedded in collagen gels
Authors: Yang Jason , Richards James , Guzman Raphael , Imagawa Walter , Nandi S.
Published: May 2006

Normal mammary epithelial cells from BALB/cfC3H midpregnant mice were freed from stromal cell types by Percoll density gradient centrifugation after collagenase digestion and were then embedded within collagen gels. Sustained growth leading to an increase in cell number was accomplished in response to cholera toxin and high concentrations of horse serum. The extent of growth was found to be dependent on the horse serum concentration, the maximum growth being attained at 50%. A serum concentration of 12.5% horse serum and 2.5% fetal calf serum, along with cholera toxin at 0.01 μg/ml, allowed maintenance but failed to cause any significant increase in cell number during the experimental period of 2 weeks. This same maintenance medium was used to determine the effects of various exogenously added steroids, protein hormones, and organ extracts on the proliferation of mammary epithelial cells in culture. Hormones failed to elicit any proliferative response, but extracts of kidney, brain, uterus, and spleen produced proliferative responses equal to or greater than the response obtained with 50% horse serum and cholera toxin. Kidney extracts prepared from midpregnant mice, virgin mice, and virgin mice given pituitary isografts all showed comparable activities, suggesting that the concentration of stimulatory factor(s) was not influenced by the hormonal status of the donor. Normal mammary epithelial cells that had undergone a 10- to 15-fold increase in cell number over initial values during 2-3 weeks in culture were passaged to secondary gel cultures. Outgrowth similar to those seen in primary culture were seen again in secondary culture. The present system provides a method for sustaining growth in culture of primary mammary epithelial cells from normal tissues.
Evidence of RNA in D loops of intracellular lambda DNA.
Authors: Chattoraj D K , Stahl F W
Published: May 2006

If lambda DNA replication is blocked by mutation in any one of several genes essential for replication, intracellular lambda DNA often shows short three-stranded regions called D loops. In this report we show that one arm of a D loop is an RNA . DNA hybrid, whereas the remaining arm is made up of single-stranded DNA. The RNA can be partially removed by RNase A and totally removed by RNase H. Also, D loops do not appear if infections are made in cells treated with rifampin, a potent inhibitor of transcription by Escherichia coli RNA polymerase. Several genes associated with recombination, including the host recA gene, are not essential for D-loop formation.
Two distinct loci confer resistance to acycloguanosine in herpes simplex virus type 1.
Authors: Coen D M , Schaffer P A
Published: May 2006

Two distinct loci that confer resistance to acycloguanosine (acyclo-Guo) in herpes simplex virus types 1 have been identified. The first locus is the gene for the virus-specific thymidine kinase (TK). Mutations that decrease TK activity also render the virus resistant to acyclo-Guo, and the level of resistance corresponds to the decrease in TK activity. acyclo-Guo resistance due to defective TK expression is recessive to the wild-type phenotype, acyclo-Guo-sensitive (ACGs). We term this locus ACGr-TK. The second locus is defined by the properties of a mutant, PAAr5, which is resistant to acyclo-Guo and to phosphonoacetic acid (PAA) yet exhibits wild-type TK activity. The acyclo-Guo-resistant locus in PAAr5 is separable from ACGr-TK mutations by recombination. Moreover, PAAr5 and ACGr-TK mutants can complement each other, producing drug-sensitive gene products which result in growth inhibition in the presence of acyclo-Guo. The acyclo-Guo resistance conferred by PAAr5 behaves as though it were codominant with the wild-type phenotype. This second acyclo-Guo-resistance locus is closely linked to the mutation specifying resistance to PAA. Resistance to PAA is thought to result from mutations in the gene for viral DNA polymerase. Thus, the close linkage of the ACGr and PAAr loci suggest that resistance to both drugs is specified by a mutant DNA polymerase. We term this second locus ACGr-PAA.
Histochemical changes in cytochrome oxidase of cortical barrels after vibrissal removal in neonatal and adult mice.
Authors: Wong-Riley M T , Welt C
Published: May 2006

The posteromedial barrel subfield of the somatosensory cortex of mice was examined histochemically for cytochrome oxidase activity (cytochrome c oxidase; ferrocytochrome c:oxygen oxidoreductase, EC 1.9.3.1). In normal mice a high enzymatic activity was found within the barrel hollows, rather than in the sides and septa. Electron microscopic examination indicated that within the hollows reactive mitochondria reside in many dendrites, in some axonal terminals, and in a few neuronal perikarya. After neonatal cauterization of selected row(s) of vibrissae, the corresponding row(s) of barrels appeared as narrowed fused band(s) and their cytochrome oxidase activity was much reduced. Removal of vibrissae in the adult, by either cauterization or repeated plucking, did not cause size changes of cortical barrels. However, there was a significant decrease in the oxidative enzymatic activity within these barrels. Thus, the deprivation of sensory input through damage to, or removal of, the peripheral sensory organ induces an enzymatic response in neurons that are at least two to three synapses away from the periphery.
Rotational propensities and identity of bond rupture in 1-cyano-2-methyl-3-(
cis
-propenyl) cyclopropanes
Authors: von Eggers Doering William , Barsa Edward A.
Published: May 2006

Comparison of the rate of recemization with the rates of diastereomerization in the title compound allows the firm conclusion to be drawn that the theoretically weakest of the three cyclopropane bonds is preferentially broken irrespective of the multiplicity of the internal rotations involved. Incidentally, the effect of an adjacent chiral methyl group on internal rotational propensities is elucidated.
Structural studies of methyl-accepting chemotaxis proteins of Escherichia coli: evidence for multiple methylation sites.
Authors: Chelsky D , Dahlquist F W
Published: May 2006

Two-dimensional analysis of tryptic peptides from [35S]methionine-labeled methyl-accepting chemotaxis proteins, MCP I and MCP II, demonstrates a high degree of homology between the two proteins. After the methylation sites were labeled with S-adenosyl-L-methyl-3H]methionine, peptides of three distinct migrations in each protein were found to carry a methyl group. These multiple methylations appear to be responsible in part for the observed multiple banding patterns on sodium dodecyl sulfate/polyacrylamide slab gels.
Sequences of two kinetoplast DNA minicircles of Tryptanosoma brucei.
Authors: Chen K K , Donelson J E
Published: May 2006

Kinetoplast DNA of Trypanosoma brucei is composed of a network of about 10,000 interlocked minicircle DNA molecules (1.0 kilobase) that are catenated with about 50 maxicircle DNA molecules (23 kilobases). Several different DNA . DNA hybridization techniques using individual minicircle DNA sequences cloned in Escherichia coli have indicated that each minicircle molecule contains about one-fourth of its sequence in common with most other minicircles and the remaining three-fourths in common with about 1 out of every 300 minicircles. We have determined the complete sequence of two cloned minicircle DNA molecules that were released from the total kinetoplast DNA network by different restriction enzymes; one minicircle is 1004 base pairs long, the other is 983 base pairs. Both are about 72% dA + dT. They share about 27% of their sequences; the largest continuous region in common is 122 base pairs of near-perfect homology. Twelve other regions of perfect homology equal to or greater than 10 base pairs are also present. Both sequences contain a large number of translation termination codons in all potential translation reading frames. The largest oligopeptide potentially specified by one minicircle sequence is 52 amino acids; the largest by the other minicircle sequence is 71 amino acids. One minicircle contains a decanucleotide sequence that is repeated in tandem five times. It is proposed that massive recombination among the interlocked minicircles in the kinetoplast DNA network may account for much of the homology observed in the two minicirce sequences.
Noninvasive
31
P NMR probes of free Mg
2+
, MgATP, and MgADP in intact Ehrlich ascites tumor cells
Authors: Gupta Raj K. , Yushok Wasley D.
Published: May 2006

31
P NMR spectra of Ehrlich ascites tumor cells, suspended in a physiological medium, show well-defined αP, βP, and γP resonances of intracellular ATP. A comparison of the separation of 360 ± 1 Hz between the resonances of αP and βP in intact cells with the corresponding separations of 349 ± 0.5 and 438 ± 1 Hz in noncellular MgATP and ATP standards, measured at 10°C and 40.5 MHz NMR frequency, reveals that 88% of the total intracellular ATP (3.3 mM) is complexed to Mg
2+
. The corresponding value for intracellular free Mg
2+
is 0.44 μmol/ml out of a total Mg
2+
content of 8.5 μmol/ml cell water. A similar value of free Mg
2+
is obtained from a comparison of the separation of 560 ± 1 Hz between the βP and γP resonances of intracellular ATP with the corresponding values of 552 ± 0.5 and 621 ± 1 Hz in noncellular MgATP and ATP standards. The fraction of total cellular ATP complexed to Mg
2+
decreased to 80% in tumor cells incubated in a medium containing adenosine, glucose, and P
i
without Mg
2+
, the corresponding level of intracellular free Mg
2+
being significantly lower (0.24 mM) than that in the unincubated cells. With Mg
2+
present in the incubation medium, MgATP and total Mg
2+
levels increased by ≈2.5 mM, whereas with no added Mg
2+
, the MgATP increased 1.6 mM apparently at the expense of other Mg
2+
-complexed constituents since total Mg
2+
remained essentially unchanged. At the measured levels of free Mg
2+
, intracellular ADP will be only 35-50% complexed to Mg
2+
. A knowledge of the state of Mg
2+
complexation of ATP and ADP in intact Ehrlich tumor cells allows an accurate estimation of the phosphorylation potential and the extent of deviation of the mass action ratio ([MgATP][AMP]
f
/[MgADP][ADP]
f
) in cells with high phosphorylation potential from the Mg
2+
-dependent equilibrium value of the adenylate kinase reaction. The significance of the free Mg
2+
value measured by the noninvasive NMR method in relation to the existence of Mg
2+
complexation and compartmentation in tumor cells is discussed.
Fate of donor insertion sequence IS1 during transposition.
Authors: Read H A , Das Sarma S , Jaskunas S R
Published: May 2006

The number of insertion sequence IS1 segments in Escherichia coli K-12 and 20 mutants in which an ISI had been inserted at a new site was measured by Southern blot hybridization analysis. The parent strain appeared to contain seven IS1 segments. Each of the mutants contained these seven IS1 and one additional IS1 corresponding to the new IS1 insertion. These results suggest that a copy of a donor ISI is inserted at the new site. A model for transposition is prevented that postulates that a reactive intermediate is formed by a tandem duplication of a transposable sequence.
Mouse fibroblast (type I) and immune (type II) interferons: pronounced differences in affinity for gangliosides and in antiviral and antigrowth effects on mouse leukemia L-1210R cells.
Authors: Ankel H , Krishnamurti C , Besançon F , Stefanos S , Falcoff E
Published: May 2006

Different interferons can be obtained from the same animal species depending on the cells and (or) the inducers used. Interferons of type I and type II differ not only antigenically but also in molecular weight and stability at low pH. We have investigated whether mouse type I and type II interferons also differ in properties relating to their biological action. We present evidence which suggests that the molecular mechanism leading to antiviral and antigrowth effects induced by both types of interferon in susceptible cells must differ in at least one important step. Antiviral and antigrowth activities of type I but not of type II interferon are both inhibited when gangliosides are added to cell cultures together with the interferon. Whereas type I interferon strongly binds to ganglioside affinity columns and can be eluted with solutions of N-acetylneuraminyllactose, type II interferon passes through such columns unretarded. L-1210 mouse leukemia cells (L-1210S) respond equally well to antiviral and antigrowth activities of type I and type II interferons. Type I interferon-resistant L-1210 cells (L-1210R), derived from L-1210S cells after continuous culture in the presence of mouse fibroblast interferon, lack antiviral and antigrowth response to mouse type I interferon [Gresser, I., Bandu, H.T. & Brouty-Boyé, D. (1974) J. Natl. Cancer Inst. 52, 553-559]. However, these cells display the same sensitivity toward type II interferon as do the parent L-1210S cells from which they were derived and respond equally well to its antiviral and antigrowth activities.
Transcription and processing of a yeast tRNA gene containing a modified intervening sequence
Authors: Johnson Jerry D. , Ogden Richard , Johnson Peter , Abelson John , Dembeck P. , Itakura Keichii
Published: May 2006

The tRNA
3
Leu
gene from yeast contains an intervening sequence of 32 nucleotides not present in mature tRNA. This sequence is transcribed and subsequently removed during the maturation of the RNA. To probe the involvement of this region of the gene in transcription and processing of the pre-tRNA
3
Leu
, the yeast DNA was cloned in plasmid pBR322 and a 21-base-pair DNA fragment corresponding to the
lac
operator was inserted into the intervening sequence. Insertion was done at a cleavage site for the restriction endonuclease
Hpa
I that occurs 19/20 base pairs from the 5′ end of the intervening sequence. The parent and modified plasmids were then transcribed in a
Xenopus
germinal vesicle extract. RNA-fingerprint analysis of the transcription products revealed that both the tRNA
3
Leu
gene and its modified counterpart were accurately transcribed. Transcription products corresponding to mature tRNA
3
Leu
and pre-RNA
3
Leu
with the normal and
lac
-containing intervening sequence were identified. Precursors extended at their 5′ and 3′ ends were also present. Both parent and modified genes were transcribed efficiently, and the various products accumulated in similar amounts, indicating that no deleterious effects on transcriptional competence, stability of the transcripts, or processing result from insertion of the 21-base-pair
lac
operator DNA. Incubation of pre-tRNA molecules that contained intervening sequences but were 5′ and 3′ mature with a yeast ribosomal wash fraction resulted in excision of the intervening sequence and, in the presence of ATP, ligation of the resulting half-tRNA molecules. The presence of RNA complementary to
lac
operator DNA neither inhibited the excision and splicing activities nor altered the site of the junction.
Induction of differentiation of murine erythroleukemia cells by aminonucleoside of puromycin and inhibition of this induction by purines and purine derivatives.
Authors: Lacour F , Harel L , Friend C , Huynh T , Holland J G
Published: May 2006

The effect of the aminonucleoside of puromycin (AMS) on Friend erythroleukemia cells in culture was investigated, because purines and purine analogues are known to act as inducers of differentiation. After treatment with 20-30 micro M AMS for 4 days, the cultures contained between 80 and 90% benzidine-positive cells. Stimulation of hemoglobin synthesis was dose and time dependent. Inosine had no stimulatory activity; however, when it was added to the medium together with AMS, erythroid differentiation was almost completely inhibited. The inhibitory effect of inosine on this potent inducer was also dose and time dependent. No cytotoxicity was observed with either compound, alone or in combination. Inhibition of AMS stimulation of erythroid differentiation was also observed in the presence of inosine monophosphate and poly(inosinic acid). Hypoxanthine had a dual effect. At high concentrations (500 microgram/ml) it acted as an inducer, but when added at low concentrations (20 microgram/ml) together with AMS it inhibited differentiation. These findings suggest there is a link between purine biosynthesis and the event(s) required to trigger differentiation. Agonist-antagonist activity of closely related biological compounds has thus been revealed in the erythroleukemia cells.
Selective amplification of variants of a complex repeating unit in DNA of a crustacean.
Authors: Christie N T , Skinner D M
Published: May 2006

The nucleotide sequence of the repeating unit of a fraction of the highly repetitive DNA of the red crab, Geryon quinquedens, is reported. Treatment of total DNA with HindIII nuclease produced an 81-base-pair monomer and multimers to the size of an octamer. Several of the multimers contained large amounts of fragments of variant sequences, which cannot easily be explained by random mutation alone. That the alterations were not random was corroborated by divergence measurements made on the distribution of Hha I nuclease sites within several multimers. The analyses showed that a fraction of each of them is characterized by 4% divergence, while the amounts of dimer, tetramer, and octamer suggest that they have undergone 2-4 times more divergence than that. These results, coupled with the data on sequence variants that are more prevalent in the dimer, indicate that amplification of divergent repeating units could easily explain enhanced amounts of selected multimers.
Expression of the immunoglobulin C mu gene in mouse T and B lymphoid and myeloid cell lines.
Authors: Kemp D J , Harris A W , Cory S , Adams J M
Published: May 2006

We have used cloned nucleotide sequences as probes to search for immunoglobulin RNA in T and B lymphoid and nonlymphoid tumor cell lines. Polyadenylated RNA from the cells was fractionated electrophoretically by size and fixed to diazobenzyloxymethyl-paper, and then immunoglobulin RNA species were revealed by hybridization with 32P-labeled cloned sequences for mu heavy chain and kappa light chain. kappa mRNA was detected only in B lymphoid lines known to synthesize kappa chains. No mu RNA was detectable in erythroleukemia, mastocytoma, or sarcoma cells. RNA bearing mu constant region (C mu) sequences, however, was detected in four of nine T lymphoma and four of five myeloid tumor cell lines tested, as well as in B lymphoma and "pre-B" Abelson lymphoma cells. In contrast to the single mu RNA species of 2.6 kilobases (kb) in a plasmacytoma, individual T lymphoma and myeloid lines yielded up to three discrete mu RNA species of apparent size 1.9, 2.2, and 3.0 kb, each different from the two mu RNA species in a B lymphoma line (2.4 and 2.7 kb) or the single species in "pre-B" lymphoma cells (2.9 kb). Both chromosomal complements of the C mu gene in STRij-4 T cells were found to be rearranged from their embryonic (germ line) context. The results suggest that the C mu gene functions not only in T cells, wherein the ability to recognize antigen is long established, but also in myeloid cells.
Phorbol esters induce differentiation in human malignant T lymphoblasts
Authors: Nagasawa Kohei , Mak Tak W.
Published: May 2006

At nanomolar concentrations, phorbol ester, a class of potent tumor promoters, can promote differentiation in the human malignant T-lymphoblastic cell line MOLT-3. The optimal dose for induction, as measured by the increase of the number of cells containing sheep erythrocyte receptors (E-rosette assay), is between 8 and 16 nM 12-
O
-tetradecanoylphorbol 13-acetate (TPA), although there were significant increases of E-rosette-positive (E
+
) cells at concentrations as low as 1.6 nM TPA. The induction was linear for 4 days, then it reached a plateau. This induction was independent of the cell densities of the cultures, and the viability of the E
+
cells remained high (95-100%) even after 10 days of culture in the presence of the tumor promoters. The E
+
cells, when measured with the more stable 2-aminoethylisothiouronium bromide E-rosette assay, indicated that virtually all (75-95%) of the MOLT-3 cells became E
+
by 4 days in culture. This induction by TPA was also accompanied by a dramatic drop in the plating efficiencies and a reduction in DNA synthesis. Examination of phorbol and other phrobol esters indicated that the ability to induce these cells correlated well with the tumor-promoting activities of these compounds, because only TPA and to a lesser extent phorbol 12,13,-dibenzoate induced E
+
cells, while phorbol and 4α-phorbol 12,13-didecanoate had no effect. Studies of MOLT-3 cells depleted of E
+
cells indicated that the induction of E
+
cells cannot be explained solely on the basis of enrichment or stimulation of the background E
+
cells in MOLT-3 cultures. Finally, we have shown that TPA also affected another differentiation marker, the loss of the enzyme terminal deoxyribonucleotidyl transferase. Terminal transferase activities and percentages of terminal-transferase-positive cells in these cultures were reduced to as low as 1/10th in 4 days in the presence of 16 nM TPA.
Electrophoretic properties of the scrapie agent in agarose gels.
Authors: Prusiner S B , Groth D F , Bildstein C , Masiarz F R , McKinley M P , Cochran S P
Published: May 2006

The molecular properties of the scrapie agent were investigated by subjecting partially purified preparations to electrophoresis on agarose gels. When electrophoresis was performed at room temperature in the presence of sodium dodecyl sulfate (NaDodSO4), most of the recoverable agent was found at the top of the gel, consistent with previous studies indicating aggregation of the agent upon exposure to elevated temperatures. In addition, less than 5% of the agent applied to the gel was found after electrophoresis, even though the study was performed with a low concentration of NaDodSO4 (0.1%). Further studies on the inactivation of the agent by NaDodSO4 suggest that this may be, in part, a function of the NaDodSO4: protein ratio in the sample. In contrast, sodium N-lauroyl sarcosinate (Sarkosyl) did not inactivate the agent in concentrations as high as 5% (wt/vol). Virtually all of the infectivity could be recovered after electrophoresis of the agent into 0.6% agarose gels at 4 degrees C in the presence of 0.2% Sarkosyl. Digestion of the preparations with micrococcal nuclease and proteinase K prior to Sarkosyl electrophoresis caused a substantial portion of the agent to migrate ahead of DNA fragments of 1 x 10(6) daltons. The behavior of the scrapie agent in electrophoretic gels is consistent with earlier studies showing that the monomeric form of the agent has a sedimentation coefficient of less than or equal to 40 S. Thus, the smallest or monomeric form of the agent is smaller than any known animal virus.
Memory neuron: synapse microchemistry for the memory component of a neuroconnective brain model.
Authors: Wooldridge D E
Published: May 2006

This paper examines the synaptic microchemistry required if a memory neuron is to have the operating characteristics previously attributed to it [Wooldridge, D.E. (1980) Proc. Natl. Acad. Sci. USA, 77,2305-2308]. It is concluded that the requirements can be met by a combination of membrane mechanisms not very different from those that are commonly postulated to explain the properties of known types of neurons.
Impulse activity of locus coeruleus neurons in awake rats and monkeys is a function of sensory stimulation and arousal.
Authors: Foote S L , Aston-Jones G , Bloom F E
Published: May 2006

By means of extracellular recordings, individual norepinephrine-containing neurons in the locus coeruleus of unanesthetized behaviorally responsive rats and squirrel monkeys were found to respond to specific sensory and behavioral conditions. In rats, distinct clusters of action potentials followed the presentation of various nonnoxious auditory, visual, or somatosensory stimuli at latencies of 15-60 msec. Increased discharge rates were also seen during periods of spontaneous electroencephalogram arousal in both species. In monkeys, these cells responded most vigorously to complex arousing stimuli such as a preferred food. Because the noradrenergic innervation of most forebrain regions arises from the locus coeruleus, these results allow prediction of situations under which this massive projection system would be active and suggest a physiological role for this chemically identified network in specific behavioral processes.
The x-ray luminosity-redshift relationship of quasars
Authors: Segal I. E. , Segal W.
Published: May 2006

Chronometric cosmology provides an excellent fit for the phenomenological x-ray luminosity-redshift relationship for 49 quasars observed by the Einstein satellite. Analysis of the data on the basis of the Friedmann cosmology leads to a correlation of absolute x-ray luminosity with redshift of >0.8, which is increased to ∼1 in the bright envelope. Although the trend might be ascribed
a priori
to an observational magnitude bias, it persists after nonparametric, maximum-likelihood removal of this bias.
Interphases of chain molecules: Monolayers and lipid bilayer membranes
Authors: Dill Ken A. , Flory Paul J.
Published: May 2006

Using the lattice model for a liquid, we treat the packing of short-chain molecules in interphases such as bilayer membranes. The constant density in the interphase imposes intermolecular constraints on the configurations of the flexible chains. The statistical theory here presented predicts a diffuse distribution of chain ends near the bilayer midplane; no adjustable parameters are required. Inasmuch as some of the chains terminate relatively near the polar interface, the number of chains reaching deeper planar layers is diminished. Consequently, configurational freedom increases with depth. This is the source of the well-known disorder gradient.
Threefolds whose canonical bundles are not numerically effective
Authors: Mori Shigefumi
Published: May 2006

Let
X
be an arbitrary nonsingular projective 3-fold whose canonical bundle is not numerically effective. Then we have: (
i
)
X
contains an exceptional divisor of several types, which we classify explicitly, (
ii
)
X
has a morphism to a projective nonsingular surface whose fibers are conics, (
iii
)
X
has a morphism to a projective nonsingular curve whose general fibers are Del Pezzo surfaces, or (
iv
)
X
is a Fano 3-fold with Picard number 1.
Electron microscopy of negatively stained and unstained fibrinogen.
Authors: Estis L F , Haschemeyer R H
Published: May 2006

Electron microscope images of negatively stained fibrinogen are predominantly asymmetric rods 450 A in length and about 60 A in width. The molecules appear to have considerable flexibility, and mass distribution along the major axis is not uniquely distinguished despite apparent beading in some particles. Scanning transmission electron microscopy of unstained fibrinogen again demonstrates that a majority of molecules are rodlike. The results differ from those obtained by negative staining in that a substantial fraction of images are trinodular with striking resemblance to those obtained by C. E. Hall and H. S. Slayter [J. Biophys. Biochem. Cytol. (1959) 5, 11--16] using the mica replica technique. The above results were obtained on glow-discharged carbon substrate films by a simple low-concentration, long-attachment-time modification of standard deposition methods that is diffusion controlled and depends on concentration and time but is independent of pH, buffer, and other staining conditions. Evidence is presented that standard attachment procedures result in artifactual images. Any models of fibrinogen in solution consequently must encompass properties that permit its visualization as an asymmetetric rod by electron microscopy as first suggested by Hall and Slayter 20 years ago.
Different pattern of codon recognition by mammalian mitochondrial tRNAs.
Authors: Barrell B G , Anderson S , Bankier A T , de Bruijn M H , Chen E , Coulson A R , Drouin J , Eperon I C , Nierlich D P , Roe B A , Sanger F , Schreier P H , Smith A J , Staden R , Young I G
Published: May 2006

Analysis of an almost complete mammalian mitochondrial DNA sequence has identified 23 possible tRNA genes and we speculate here that these are sufficient to translate all the codons of the mitochondrial genetic code. This number is much smaller than the minimum of 31 required by the wobble hypothesis. For each of the eight genetic code boxes with four codons for one amino acid we find a single specific tRNA gene with T in the first (wobble) position of the anticodon. We suggest that these tRNAs with U in the wobble position can recognize all four codons in these genetic code boxes either by a "two out of three" base interaction or by U.N wobble.
Recognition of chemical carcinogen-modified DNA by a DNA-binding protein.
Authors: Moranelli F , Lieberman M W
Published: May 2006

Using a filter binding assay, we have detected and partially purified a protein from human placenta that has a high affinity for N-acetoxy-2-acetylaminofluorene-modified double-stranded DNA (AAF-[3H]DNA) of bacteriophage T7. This protein has been partially purified from a 1 M NaCl extract of a crude nuclear fraction by a combination of ion-exchange and nucleic acid affinity chromatography. With AAF-[3H]DNA as the substrate, the binding reaction reached equlibrium within 1 hr at 4 degrees C, and the extent of binding ws proportional to the amount of protein added. Complex formation was dependent on both pH and salt concentration and was unaffected by the presence of sulfhydryl-blocking agents. The purest protein fraction also recognizes DNA modified with methylmethane-sulfonate or methylnitrosourea. It shows little or no recognition of single-stranded DNA, double-stranded DNA, supercoiled bacteriophage phiX174 DNA, partially depurinated DNA, glucosylated bacteriophage T4DNA, or UV-irradiated DNA. No endo- or exonuclease activity, DNA polymerase activity, or glucosylase activity for AAF-DNA was detectable in the preparation.
Integrative recombination of bacteriophage lambda: extent of the DNA sequence involved in attachment site function.
Authors: Mizuuchi M , Mizuuchi K
Published: May 2006

We have investigated the minimum extent of DNA sequence required for the attachment site of bacteriophage lambda to function in integrative recombination. A DNA fragment carrying the phage attachment site (attP) of bacteriophage lambda was trimmed, recloned, and tested for recombination proficiency. In order to recombine with the bacterial attachment site (attB), the phage attachment site must retain about 250 base pairs of its original sequence. On the left side, the essential sequence extends beyond 106 base pairs from the center of the 15-base-pair common core sequence but not beyond 152 base pairs. On the right side the required sequence extends beyond 68 base pairs but not beyond 99 base pairs from the center of the core. A trimmed site that has lost part of the sequence mentioned above cannot function as the phage attachment site. However, depending on which part of the sequence is present, such a site can still act in reactions normally requiring one of the prophage attachment sites or the bacterial attachment site. The results also suggest that the essential suquence of the bacterial attachment site consists only of the sequence common to the phage and bacterial attachment sites.
Amino acid sequence of the variable region of a human mu chain: location of a possible JH segment.
Authors: Lehman D W , Putnam F W
Published: May 2006

The complete amino acid sequence of th variable (V) region of the mu heavy chain of a human IgM immunoglobulin (Cam) has been determined. The strategy for sequence determination involved sequenator analysis of the CNBr cleavage products of the succinylated carboxymethylated Fab mu fragment, and of tryptic peptides of the CNBr polypeptides and thermolytic subpeptides. The variable region of this heavy chain (VH) belongs to the VHIII subgroup; it has greater than 70% homology with other VHIII sequences and contains the VHIII marker peptide, Phe-Thr-Ile-Ser-Arg (residues 67-71). As more sequences have been published, the number of subgroup-specific residues has diminished to the point that no position is absolutely subgroup specific. An analysis of the available human VH sequences in the V/C switch region showed the likelihood of a human JH segment (residues 101-113) analogous to the J segments in mouse light chains. The JH region is highly conserved, has striking homology to proposed mouse JH regions, and has significant homology to known mouse J lambda and J kappa segments.
Cadmium-113 NMR of carbonic anhydrases: effect of pH, bicarbonate, and cyanide.
Authors: Jonsson N B , Tibell L A , Evelhoch J L , Bell S J , Sudmeier J L
Published: May 2006

113Cd-Substituted human and bovine erythrocyte carbonic anhydrases have been studied by 113Cd NMR as a function of pH and bicarbonate concentration. Plots of chemical shift versus pH give sigmoidal titration curves in the pH range of the study, 6.9 to 10.5. The pKa values vary from 9.2 to 9.7, which correlates well with available activity profiles for the Cd-enzymes. Because the samples contain no buffers and no anions other than hydroxide, the results point to the existence of high and low pH forms of the enzymes in rapid exchange and differing in inner sphere coordination. When bicarbonate is added to the samples, upfield shifts are produced which eventually level off. Only a single CN- binds to the metal for all three enzymes. These observations are best explained by a rapid exchange among three species in which the open coordination site of the metal ion is occupied by hydroxide, water, or bicarbonate, as in the scheme: E--OH- in equilibrium or formed from E--H2O in equilibrium or formed from E--HCO-3.
Nucleotide sequence of Moloney leukemia virus: 3' end reveals details of replications, analogy to bacterial transposons, and an unexpected gene.
Authors: Sutcliffe J G , Shinnick T M , Verma I M , Lerner R A
Published: May 2006

We have determined the sequence of a cloned DNA fragment 1108 base pairs long which corresponds to the 3' end of the Moloney murine leukemia provirus. The clone was obtained as the primary product of reverse transcription and begins with the Moloney "strong stop" sequence, then extends towards the 5' end of the provirus. Our sequence: (i) proves that reverse transcriptase switches templates during minus strand synthesis; (ii) defines the limits of the 515-base-pair repeats which occupy both ends of the integrated provirus; (iii) shows that the structure of the proviral repeats has strong analogy to bacterial insertion sequences, indicating that the Moloney provirus is a transposon; (iv) identifies the putative promotor for genomic transcription within these repeats; (v) shows that the presumed origin of second strand synthesis, which lies just outside the 3' repeat, has tertiary structure analogous to single-stranded bacteriophage origins of replication; (vi) solves the amino acid sequence of most of pI5E, the carboxy-terminal product of the env gene; (vii) allows detailed mapping of the mink cell focus-forming virus substitution locus in a central location within the gp70 region of the env gene; and (viii) identifies a long open translation frame to the right of the env gene (R gene) which could be involved in leukemogenesis.
Conformational changes during enzyme catalysis: role of water in the transition state.
Authors: Loftfield R B , Eigner E A , Pastuszyn A , Lövgren T N , Jakubowski H
Published: May 2006

The entropy of activation for the synthesis of Ile-tRNA is high and positive. The only likely source of a high delta S is the loss of structured water as the enzyme . substrate complex moves toward the transition state. This requires a change in the orientation or nature of water-organizing residues in the interface between the enzyme . substrate complex and the water. Such changes, which may be some distance from the "active site," are coupled to the active site in such a way that the increased entropy and decreased free energy of the water--enzyme interface is available at the "active site" to reduce the free energy of activation. The effects of Hofmeister anions on KmS and KcatS are consistent with the entropy data.
Activation of human beta-globin genes from nonerythroid cells by fusion with murine erythroleukemia cells.
Authors: Pyati J , Kucherlapati R S , Skoultchi A I
Published: May 2006

A human beta-globin gene derived from an established human lymphoblast cell line was introduced into murine erythroleukemia (MEL) cells by cell fusion. The globin genes in MEL cells are inducible by dimethyl sulfoxide (Me2SO); induction leads to the accumulation of mouse globin mRNA and hemoglobin. Globin mRNA was not detected in the cytoplasm of the human lymphoblast cells, even at low levels, whether or not these cells were treated with Me2SO. In cell hybrids that had retained the lymphoblast-derived beta-globin gene, human beta-globin mRNA was induced by Me2SO. Poly(A)-containing 10S human beta-globin mRNA was detected in the cytoplasm of the hybrid cells. Karyologic and isozymic analyses of a series of hybrids and subclones showed that human beta-globin gene expression occurred only in hybrids that had retained human chromosome 11. Analysis of one hybrid bearing a deletion of both the beta-globin and lactate dehydrogenase A genes indicated that the beta-globin gene is located on the short arm of human chromosome 11. No other human chromosomes are required for human beta-globin gene expression in MEL cell hybrids. We conclude that the restricted expression of a globin gene in a human nonerythroid cell can be reversed. Furthermore, all components required for the transcription, processing, and transport to the cytoplasm of a human globin mRNA appear to be present in mouse erythroleukemia cells. Thus cell fusion with MEL cells provides a way to isolate permanent cell lines with functioning human globin genes. The technique should be useful for studying the biochemical basis for abnormal function of mutant globin genes, such as those present in individuals with the thalassemia syndromes.
Differential expression of type I and type II cyclic AMP-dependent protein kinases during cell cycle and cyclic AMP-induced growth arrest.
Authors: Haddox M K , Magun B E , Russell D H
Published: May 2006

The activation state of cyclic AMP-dependent protein kinase(s)(ATP:protein phosphotransferase, EC 2.7.1.37) is transiently increased 2-fold as a function of G1 progression in mitotically synchronized Chinese hamster ovary cells. The cellular content of type I kinase increases concomitantly with the increase in general protein, whereas the activity of type II kinase increases as a function of time in G1 to a maximum at the G1/S border. In contrast, in the presence of dibutyryl-cyclic AMP, there is a decrease of type II kinase and a several-fold increase of type I kinase. In proliferating cells, the ratio of type I to type II was 0.37, while in the dibutyryl-cyclic AMP growth-arrested cells it was 3.96. The increase in type II kinase during G1 transition and the increase in type I kinase during dibutyryl-cyclic AMP treatment were dependent on protein synthesis. A similar pattern of type I and type II kinase expression during cell cycle progression occurred in Rat-1 fibroblasts and Rat-1 cells transformed by Rous sarcoma virus. The inclusion of dibuityryl-cyclic AMP in the growth media promoted a marked increase in type I holoenzyme, which was inhibited by cycloheximide, and a decrease in type II kinase. Neither AMP nor sodium butyrate had any effect on cellular kinase levels, whereas 8-bromo-cyclic AMP mimicked the action of dibutyryl-cyclic AMP. Estimation of half-lives for the kinase types showed that there was little turnover of either type during normal G1 progression, rapid turnover of both types as cells exited from mitosis, and selective turnover of type II upon addition of dibutyryl-cyclic AMP.
Feedback regulation of ribosomal protein gene expression in Escherichia coli.
Authors: Dean D , Nomura M
Published: May 2006

The structural genes for Escherichia coli ribosomal protein (r-protein) genes L1, S4, and S11 were inserted into a plasmid vector containing the lac operator and promoter such that the synthesis of L1, S4, and S11 was controlled by lac regulatory elements. Synthesis of L1, S4, and S11 was stimulated by addition of an inducer of the lac operon (isopropyl thiogalactoside) to exponentially growing cells. Elevated synthesis of L1 caused a specific decrease in L11 synthesis, whereas overproduction of S4 resulted in lowered synthesis of S13 and L17. Stimulation of L1 or S4 synthesis also inhibited cell growth. Overproduction of S11 did not affect synthesis of other r-proteins or alter growth. These results confirm previous in vitro studies [Yates, J. L., Arfsten, A. E. & Nomura, M. (1980) Proc. Natl. Acad. Sci. USA 77, 1837-1841] and support the hypothesis that certain r-proteins have the capacity to selectively inhibit synthesis of r-proteins whose genes are in the same operon as their own.
Polymorphism in mitochondrial DNA of humans as revealed by restriction endonuclease analysis.
Authors: Brown W M
Published: May 2006

Mitochondrial DNA samples from each of 21 humans of diverse racial and geographic origin were digested with each of 18 restriction endonucleases. The sizes of the resulting DNA fragments were compared after gel electrophoresis. No differences among the samples were detected in digest with 7 of the enzymes. Analysis of digests with the remaining enzymes showed one or more differences. Each of the 21 samples could be characterized individually on the basis of these digests. All between-sample differences could be explained by single base substitutions. No evidence for sequence rearrangements (inversions, transpositions) was obtained. Fourteen of the site alterations were shared by two or more samples; six of these were shared between races. The data indicate that individuals differ from a postulated ancestral mtDNA sequence at 0.18% of their base pairs. On the basis of an estimated rate for base substitution of 1% per 10(6) years [Brown, W. M., George, M., Jr. & Wilson, A. C. (1979) Proc. Natl. Acad. Sci. USA 76, 1967-1971], Homo sapiens could have speciated or passed through a severe population constriction as recently as 180,000 years ago. The data suggest that group-specific patterns of cleavage exist. The high resolution and precision afforded by this method of analysis makes possible the investigation of many questions concerning human population genetics, evolution, and recent history.
Stage-specific proteins and glycoproteins of plasmodium falciparum: identification of antigens unique to schizonts and merozoites.
Authors: Kilejian A
Published: May 2006

Establishment of highly synchronized cultures of Plasmodium falciparum enabled identification of stage-specific proteins, glycoproteins, and antigens. Comparison of metabolically labeled constituents of rings, trophozoites, mature schizonts, and merozoites indicated the absence of major proteins or glycorproteins unique to rings or trophozoites. A burst of new synthetic activity occurred during schizogony when several schizont- and merozoite-specific proteins and glycoproteins became apparent. In addition to the knob protein, which was previously shown to be associated with protrusions on the host erythrocyte membrane, a major glycoprotein of parasite origin was identified on the surface membrane of schizonts. Analysis of antigens solubilized from different developmental stages indicated that immune sera, which inhibit growth of parasites in vitro, react mainly with merozoite- and schizont-associated antigens.