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Biomedical subjects

K B Jacobson

Publications and source records attributed to K B Jacobson.

At least 73 records · Page 4Linked to original sources
PubMed1981

Presence of queuine in Drosophila melanogaster: correlation of free pool with queuosine content of tRNA and effect of mutations in pteridine metabolism.

Queuine, a modified form of 7-deazaguanine present in certain transfer RNAs, is shown to occur in Drosophila melanogaster adults in a free form and its concentration varies as a function of age, nutrition and genotype. In several, but not all mutant strains, the concentrations of queuine and the Q(+) (queuine-containing) form of tRNATyr are correlated. The bioassay employs L-M cells which respond to the presence of queuine by an increase in their Q(+)tRNAAsp that is accompanied by a decrease in the Q(-)tRNAAsp isoacceptors. The increase in Q(+)tRNATyr in Drosophila that occurs on a yeast diet is accompanied by an increase in queuine. Similarly the increase of Q(+)tRNAs with age also is accompanied by an increase in free queuine. In two mutants, brown and sepia, these correlations were either diminished or failed to occur. Indeed, the extract of both mutants inhibited the response of the L-M cells to authentic queuine. When the pteridines that occur at abnormally high levels in sepia were used at 1 x 10(-6)M, the inhibition of the L-M cell assay occurred in the order biopterin greater than pterin greater than sepiapterin. These pteridines were also inhibitory for the purified guanine:tRNA transglycosylase from rabbit but the relative effectiveness then was pterin greater than biopterin greater than sepiapterin. Pterin was competitive with guanine in the enzyme reaction with Ki = 0.9 x 10(-7)M. Also when an extract of sepia was chromatographed on Sephadex G-50, the pteridine-containing fractions only were inhibitory toward the L-M cell assay or the enzyme assay. These results indicate that free queuine occurs in Drosophila but also that certain pteridines may interfere with the incorporation of queuine into RNA.

Animals↗
PubMed1980

The interaction of cadmium and certain other metal ions with proteins and nucleic acids.

The toxic effects of cadmium and other selected divalent cations are presumed to be related to specific chemical and physical characteristics of the ion. The chemistry of cadmium and metal ions in general is reviewed from the viewpoint of such relevant properties as ion polarizability, electronic structure, and the hard-soft characteristics. The softness of metal ions is seen as a useful single parameter to correlate with the affinity for nucleic acids and proteins and with toxic effects. The effects of cadmium on nucleic acids and proteins are examined for a number of specific cases to illustrate the variety of interactions that are well recognized and to demonstrate the utility of soft metal ions as reagents and probes for examining the relationship of structure and function in these macromolecules.

Amino Acids↗
PubMed1979

Biosynthesis of "drosopterins" by an enzyme system from Drosophila melanogaster.

The red eye pigment of Drosophila melanogaster consists of six complex pteridines known as neodrosopterin, drosopterin, isodrosopterin, fraction e, and aurodrosopterins (2); these pigments are greatly reduced in the purple mutant. Conditions for biosynthesis of these "drosopterins" are described and compared with those for the synthesis of sepiapterin. The enzymes are contained in a soluble, pteridine-free extract obtained between 40 and 60% saturated ammonium sulfate. The results indicate that sepiapterin synthase consists of two enzymes, the first of which provides a precursor for "drosopterin" biosynthesis. The evidence is (1) the purple mutant, low in accumulated sepiapterin and "drosopterins", is known to have approximately 10% of the sepiapterin synthase activity of wild type; (2) unlabeled sepiapterin does not cause isotope dilution of "drosopterin" synthesis; (3) the 600g pellet prepared from a wild-type head homogenate contains "drosopterin" synthesizing activity and no sepiapterin synthase, yet a heat-labile factor in this fraction stimulates sepiapterin synthesis in the 100000g supernatant of wild-type or pr flies; (4) sepiapterin and "drosopterin" syntheses require Mg2+; (5) sepiapterin synthesis is stimulated by NADPH; "drosopterin" synthesis responds to either NADPH or NADH. Although "drosopterins" are complex pteridine-type pigments, we have demonstrated their biosynthesis by soluble enzymes. This allows us to consider investigation into the mechanism by which the amounts of these pigments are regulated.

Animals↗
PubMed1979

Developmental changes of sepiapterin synthase activity associated with a variegated purple gene in Drosophila melanogaster.

A variegated position effect on the autonomous gene, purple, has been studid enzymologically in Drosophila melanogaster. Sepiapterin synthase, the enzyme system associated with pr+, was examined for activity in different developmental stages of the fly. The results indicate that T(y:22)prc5, cn/prc4 cn flies (flies in which pr+ has been translocated and which exhibit variegation) have a reduced amount of enzyme activity as compared with both Oregon-R and pr1 flies. This reduction in activity was not found in larval stages, which suggests that the inactivation process probably occurs in late larval or early pupal stages. The phenotype of the variegated adult has white eyes with red-colored spots and patches where drosopterins occur. The phenotype of the fly carrying the translocation is modified by the presence of additional Y chromosomes. This extends the observation from other systems that extra heterochromatin acts to suppress the variegated position effect. The advantages of studying the variegation by measuring enzyme activity, as well as the phenotypic expression, are several; for example, the developmental time at which variegation occurs may be estimated even though drosopterin synthesis is not occurring.

Animals↗
PubMed1979

Alteration of the Q family of transfer RNAs in adult Drosophila melanogaster as a function of age, nutrition, and genotype.

Four tRNAs are known to contain Q, a hypermodified form of guanosine, in one of their isoacceptor forms; these are tRNATyr, tRNAHis, tRNAAsp, and tRNAAsn. The first three have been examined in Drosophila melanogaster at different ages in four genotypes. As the adult flies age, the ratio of the Q/non-Q isoacceptors increases, and the rate of increase is more rapid for Samarkand than for Oregon-R (two wild-type strains). Similarly, two other strains that carry the mutations su(s)2 v; bw and v; bw also differ in the rate of isoacceptor alteration. Diet has a marked effect on the ratio of Q/non-Q isoacceptors for each tRNA. tRNALeu does not change with age or diet and is believed not to contain Q in any of its isoacceptors. The possible role of Q in altering the rate of protein synthesis was examined in a cell-free, tRNA-dependent, mRNA-dependent system. No essential effect on the rate or extent of protein synthesis was detected upon comparison of Q-enriched or Q-deficient tRNA. The ratio of Q/non-Q isoacceptors for these tRNAs is clearly controlled by age-related and diet-related mechanisms that can modulate the amount of Q in the tRNA. The relationship of these studies to Strehler's hypothesis of age-related control of protein synthesis is discussed.

Aging↗
PubMed1978

Mechanism of suppression in Drosophila. VII. Correlation between disappearance of an isoacceptor of tyrosine tRNA and activation of the vermilion locus.

The possibility that tyrosine tRNA modifies the catalytic activity of tryptophan oxygenase that is produced by the vermilion mutant (v) in Drosophila melanogaster is reconsidered. Dietary conditions can modify the ratio of the two major isoacceptors of tyrosine tRNA: one condition allows 85--90% to exist as the second isoacceptor, and another condition allows less than 5% to exist in this form. The function lacking in the vermilion mutant is partially restored when the second isoacceptor of tRNATyr is reduced to low levels (less than 40%), but the function is greatly reduced when this isoacceptor is present as 50% or more of the total. These data support the hypothesis that tRNATyr may be associated with and regulate tryptophan oxygenase. The corresponding isoacceptor of tRNATyr found in a suppressor mutant, su(s)2, should not have any effect on the function of the vermilion gene, and, indeed, it did not. The tRNAs for tyrosine, aspartic acid, and histidine all have one isoacceptor that contains nucleoside Q and all undergo parallel changes in flies raised on the various diets. It appears that these dietary changes affect the ability to synthesize or modify Q or to remove or insert it into tRNA.

Animals↗
PubMed1978

Multiple isoacceptor forms of several transfer ribonucleic acids in a mutant yeast strain.

By use of reverse phase 5 chromatography, a strain of Saccharomyces cerevisiae (XB 109-5B) has been shown to exhibit multiple isoaccepting forms for several of the transfer ribonucleic acids (tRNAs). This is in contrast with a standard wild-type strain where only one acceptor is found for each tRNA studied. Multiple peaks for tRNATyr, tRNAPhe, tRNASer, and tRNAVal have been detected for strain XB 109-5B. However, the observation of multiple isoacceptors cannot be extended to all tRNAs in this strain since tRNAAsp appears as a single form that is the same as in the wild type. The appearance of multiple peaks was found to depend on the growth conditions of the cells. The tRNA profiles of XB 109-5B that was grown rapidly with vigorous aeration differed the most from profiles of comparably grown wild-type yeast, whereas tRNA from this mutant, grown without shaking or supplementary aeration, appeared the same as the wild type. The minor nucleoside composition of the isoacceptors of tRNAPhe was obtained.

Amino Acyl-tRNA Synthetases↗
PubMed1977

Mechanism of suppression in Drosophila: control of sepiapterin synthase at the purple locus.

The amounts of sepiapterin and red pteridine eye pigments (drosopterins) in Drosophila melanogaster are known to be reduced in the purple mutant and restored to normal by a suppressor mutation. We show here that sepiapterin synthase activity is 30 percent of normal in pr and prbw, two naturally occurring alleles of purple, and is restored to nearly normal levels by the suppressor su(s)2. A heterozygote of two newly induced alleles of pr has even lower enzyme activity (less than 10 percent). The sepiapterin synthase activity is proportional to the number of wild-type pr alleles in flies when one and two copies of the allele are present and is higher in three-than in two-dose flies. We hypothesize that the purple locus may be a structural gene for sepiapterin synthase in Drosophila.

Alcohol Oxidoreductases↗
PubMed1977

Isolation and characterization of pteridines from heads of Drosophila melanogaster by a modified thin-layer chromatography procedure.

An improved thin-layer chromatography technique is described for the separation of fluorescent compounds found in extracts of heads of Drosophila melanogaster. Eighteen to twenty fluorescent spots are resolved, two of which are xanthurenic acid and 3-hydroxykynurenine, and the remaining spots are presumably pteridines. Of these, nine have been identified and quantitated directly on the chromatograms with a fluorometer. One of the spots present on the chromatogram apparently has not been described previous to this work. Characteristics of this substance, termed "quench spot," are presented, several of which indicate that it may be a pteridine or pteridine derivative.

Animals↗
PubMed1977

Mechanism of suppression in Drosophila. V. Localization of the purple mutant of Drosophila melanogaster in the pteridine biosynthetic pathway.

The suppressible eye color mutant purple (pr) of Drosophila melanogaster is known to be unable to synthesize a wild-type complement of pteridine eye pigments. This study measures the reduced levels of drosopterins, sepiapterin, and an unidentified presumed pteridine in pr and prbw. Pteridine analyses in double mutants combining pr with one of three other eye color mutants sepia, Henna-recessive3, and prune2, suggest that the metabolic block in pr occurs prior to sepiapterin biosynthesis. Measurements of GTP and GTP cyclohydrolase in pr showed wild-type levels and indicate the metabolic block in pr to be at one of the steps converting dihydroneopterin triphosphate to sepiapterin. Quantitation of pteridines in suppressed purple [su(s)2; pr and pr; su(pr)e3] shows restoration of pteridines to wild-type or nearly wild-type levels.

Aging↗
PubMed1976

A nonspecific inhibitory effect of tRNA on the activity of 3-deoxy-D-arabino-heptulosonate-7-phosphate synthase from Saccharomyces cerevisiae.

The inhibitory effect of tRNA on yeast 3-deoxy-D-arabino-heptulosonate-7-phosphate (DAHP) synthase (EC 4.1.2.15) has been reinvestigated. From earlier studies the inhibition by tRNAPhe appeared to be quite specific. This study shows that tRNAPhe is indeed a potent inhibitor but so is unfractionated tRNA, as well as ribosomal RNA and heparin. Complete digestion to mononucleotides relieves the inhibition. Since the enzyme requires a metal ion (Co2+) we suggest that the RNA and heparin are inhibitory by virtue of their capacity to chelate the Co2+.

3-Deoxy-7-Phosphoheptulonate Synthase↗
PubMed1976

Radiation-induced mutations at mouse hemoglobin loci.

In experiments designed to detect new mutations affecting hemoglobin, we irradiated the male or female parent in reciprocal crosses of two mouse strains that differ in alleles at the hemoglobin (Hba, Hbb) loci as well as at five other specific loci. Offspring were analyzed for hemoglobin properties (electrophoretic pattern, solubility, crystal pattern), serum albumin differences, erythrocyte lysis, reticulocyte count, and external appearance. Five hemoglobin variants were found among the mutants. In three, the genetic contribution from the irradiated father was not expressed with regard to the alpha-chain; one carried a tandem deuplication (the first known case in the mouse) involving Hbb; and one probably resulted from double nondisjunction of chromosome 7. The finding that major chromosome aberrations can mimic hemoglobin mutations indicates the need, in similar experiments, to follow F1 screening with thorough cytogenetic analysis. The variants in which there is nonexpression of the alpha chain may be the result of small deficiencies or of faults in transcription or translation. Mutation rates based on these three variants are not out of line with earlier specific-locus results, although confidence limits are still wide.

Anemia↗
PubMed1976

Mechanisms of suppression in Drosophila. IV. Specificity and properties of tyrosyl-tRNA synthetase.

Tyrosyl-tRNA synthetase from wide type Drosophila can distinguish tRNATyr of wild type from that of the suppressor mutant, su(s)2. The method of fractionation of the enzyme on DEAE-cellulose can produce three different forms of the enzyme. One of these forms is characterized in this study. We describe the apparent Km for K+, Mg2+, ATP, tyrosine and tRNA, as well as its heat stability and molecular weight. Spermine does not replace Mg2+ but is inhibitory, a Ki of 1 mM was obtained. Inhibition by p-chloromercuribenzoate results in a Ki of 1 muM. The properties of tyrosyl-tRNA synthetase of Drosophila are compared to the properties of this enzyme from E. coli, B. subtilis and yeast.

Amino Acyl-tRNA Synthetases↗