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M Zasloff

Publications and source records attributed to M Zasloff.

At least 73 records · Page 4Linked to original sources
PubMed1989

Effects of magainins and cecropins on the sporogonic development of malaria parasites in mosquitoes.

Magainins and cecropins are families of peptides with broad antimicrobial and antiparasitic activities derived respectively from the skin of frogs or from giant silk moths. In insects, cecropins function as part of an inducible immune system against a number of bacterial infections. When injected into anopheline mosquitoes previously infected with a variety of Plasmodium species, both magainins and cecropins disrupt sporogonic development by aborting the normal development of oocysts; sporozoites are not formed and the vector cannot transmit the parasite to another host. It may be possible to induce effective transmission-blocking immunity in the mosquito vector by the introduction and expression of genes coding for magainins, cecropins, or similarly acting parasiticidal peptides into the mosquito genome.

Animals↗
PubMed1988

Antimicrobial properties of peptides from Xenopus granular gland secretions.

Previously, we described a family of novel broad spectrum antimicrobial peptides, magainins, from the skin of Xenopus laevis. In this report we show that at least two other Xenopus peptides, present in the skin and its secretions, PGLa and a peptide released from the xenopsin precursor, exhibit antimicrobial properties comparable to the magainins. The identification of these newer members provides insight into the structural diversity of vertebrate antimicrobial peptides.

Amino Acid Sequence↗
PubMed1988

A two-dimensional NMR study of the antimicrobial peptide magainin 2.

Using two-dimensional NMR spectroscopy, a complete 1H resonance assignment has been obtained for the peptide magainin 2 recently isolated from Xenopus laevis. It is demonstrated that this peptide adopts an alpha-helical structure with amphiphilic character when dissolved in a mixture of trifluoroethanol (TFE) and H2O. The transition to the alpha-helical conformation occurs at very low concentrations of TFE.

Animals↗
PubMed1988

Antimicrobial activity of synthetic magainin peptides and several analogues.

We have previously reported the isolation of two broad-spectrum antimicrobial peptides ("magainins") from the skin of the African clawed frog Xenopus laevis. These natural peptides are active against many species of bacteria and fungi and also induce osmotic lysis of protozoa. In this report we demonstrate that synthetic magainin peptides appear to be indistinguishable from the natural products with respect to chromatographic properties and biological activity. These studies demonstrate conclusively that the magainin peptides are potent antimicrobial substances.

Animals↗
PubMed1988

Pathway of B1-Alu expression in microinjected oocytes: Xenopus laevis proteins associated with nuclear precursor and processed cytoplasmic RNAs.

We have previously characterized B1-Alu gene expression by microinjected Xenopus laevis oocytes. The transcription, endonucleolytic processing and its kinetics, nuclear transport kinetics, and subsequent cellular compartmentalization have been described previously (Adeniyi-Jones and Zasloff, Nature 317:81-84, 1985). Briefly, a B1-Alu gene is transcribed by RNA polymerase III to a 210-nucleotide (210nt) primary transcript which is processed to yield 135nt and 75nt RNAs. After processing, the 135nt RNA enters the cytoplasmic compartment, where it remains stable, while the 75nt RNA is degraded. In this report we characterize this pathway further and show that the RNAs involved are complexed with specific X. laevis proteins. The primary transcript was associated with an X. laevis protein of 63 kilodaltons (p63) as well as La, a protein known to be associated with RNA polymerase III transcripts. After processing, the cytoplasmic 135nt RNA remained associated only with the X. laevis p63 in the form of a small ribonucleoprotein. Human autoimmune antibodies were purified by affinity chromatography to X. laevis p63 and used to immunoprecipitate human ribonucleoprotein containing a 63-kilodalton polypeptide and small RNAs. These data suggest that Alu-analogous ribonucleoproteins and their metabolic pathways are conserved across species and provide insight as to their possible functions.

Animals↗
PubMed1987

Enhancement of mRNA nuclear transport by promoter elements.

This report describes studies on the kinetics of herpes thymidine kinase (TK) mRNA transport in X. laevis oocytes as studied by microinjection and microdissection. We show that TK mRNA nuclear transport in this cell can be dramatically altered by introduction of specific DNA sequences into the nucleus. Introduction of DNA sequences encompassing the promoter results in enhancement, in trans, of a transport process that can deliver previously synthesized RNA to the cytoplasm. The report suggests that the promoter of a eukaryotic gene can functionally interact with the mechanism involved in mRNA nuclear transport.

Animals↗
PubMed1987

Magainins, a class of antimicrobial peptides from Xenopus skin: isolation, characterization of two active forms, and partial cDNA sequence of a precursor.

A family of peptides with broad-spectrum antimicrobial activity has been isolated from the skin of the African clawed frog Xenopus laevis. It consists of two closely related peptides that are each 23 amino acids and differ by two substitutions. These peptides are water soluble, nonhemolytic at their effective antimicrobial concentrations, and potentially amphiphilic. At low concentrations they inhibit growth of numerous species of bacteria and fungi and induce osmotic lysis of protozoa. The sequence of a partial cDNA of the precursor reveals that both peptides derive from a common larger protein. These peptides appear to represent a previously unrecognized class of vertebrate antimicrobial activities.

Amino Acid Sequence↗
PubMed1987

Unique pathway of expression of an opal suppressor phosphoserine tRNA.

An opal suppressor phosphoserine tRNA gene is present in single copy in the genomes of higher vertebrates. We have shown that the product of this gene functions as a suppressor in an in vitro assay, and we have proposed that it may donate a modified amino acid directly to protein in response to specific UGA codons. In this report, we show through in vitro and in vivo studies that the human and Xenopus opal suppressor phosphoserine tRNAs are synthesized by a pathway that is, to the best of our knowledge, unlike that of any known eukaryotic tRNA. The primary transcript of this gene does not contain a 5'-leader sequence; and, therefore, transcription of this suppressor is initiated at the first nucleotide within the coding sequence. The 5'-terminal triphosphate, present on the primary transcript, remains intact through 3'-terminal maturation and through subsequent transport of the tRNA to the cytoplasm. The unique biosynthetic pathway of this opal suppressor may underlie its distinctive role in eukaryotic cells.

Biological Transport↗
PubMed1986

Eukaryotic pre-tRNA 5' processing nuclease: copurification with a complex cylindrical particle.

In eukaryotes pre-tRNA species are processed at the 5' end by an endonuclease. Here we describe the first characterization of the structure of a eukaryotic pre-tRNA 5' processing endonuclease. The 5' pre-tRNAase, isolated from X. laevis ovaries, copurifies with a 16S macromolecular complex consisting of at least 14 polypeptides ranging in MW from about 20,000 to 32,000. These polypeptides comprise a cylindrical particle, apparently organized as a stack of four rings, similar or identical to a ubiquitous eukaryotic subcellular particle described in the literature over the past 15 years. Similar copurification is observed for the enzyme from HeLa cells, suggesting that the X. laevis enzyme is representative of a general class of eukaryotic pre-tRNA 5' processing nuclease.

Animals↗
PubMed1986

Limited dermal ossification: clinical features and natural history.

For 9 years we have observed a girl who has ossification in the dermis with a strikingly limited distribution. Recently a second girl with similar dermal ossification restricted to a single extremity was identified. The ectopic bone is histologically identical to normal membranous bone. These two patients have no obvious underlying cause for soft tissue bone formation, and no disorder of calcium or phosphate metabolism. Ossification first involved the dermal and subcutaneous connective tissue, and with time advanced locally in the affected areas to bridge joints and limit mobility. The ossification has now extended to involve muscle fascia but has not involved the muscle itself. This disease appears to represent a heretofore unrecognized disorder of mesenchymal differentiation.

Bone and Bones↗
PubMed1985

Purification and characterization of an endonuclease from Xenopus laevis ovaries which accurately processes the 3' terminus of human pre-tRNA-Met(i) (3' pre-tRNase).

We have previously reported that the primary transcript of the human tRNAMeti gene undergoes accurate processing to a mature 72-nucleotide species by activities present in the high speed supernatant of Xenopus laevis ovarian extracts (Zasloff, M., Santos, T., Romeo, P., and Rosenberg, M. (1982a) J. Biol. Chem. 257, 7857-7863). We now report the purification and characterization of the enzyme which processes the 3' terminus of the human pre-tRNAMeti species. The activity has been purified about 500-fold from a high speed supernatant of X. laevis ovarian extracts by standard methods. It appears to function as a single polypeptide with a molecular weight of about 97,400. The enzyme generates the mature 3' terminus with a single endonucleolytic cut, also yielding the intact 3' trailer. The endonuclease has a striking preference for the 5' processed pre-tRNAMeti, exhibiting little or no activity in vitro on the intact primary transcript. The enzyme acts similarly with the pre-tRNAAla species of Bombyx mori, suggesting that it possesses a broad substrate range. The requirement of the 3' processing endonuclease for a processed 5' terminus suggests that eukaryotic pre-tRNA processing should follow an ordered cutting sequence in vivo with processing of the 5' leader preceding 3' end maturation.

Animals↗
PubMed1985

tRNA nuclear transport: defining the critical regions of human tRNAimet by point mutagenesis.

We recently described a carrier-mediated nuclear transport system for tRNA in Xenopus laevis oocytes. A natural human tRNAimet variant with a G to T transversion in position 57 is defective in transport across the nuclear membrane. In addition, processing of the primary transcript of the variant gene is much less efficient than the wild type. We now describe the nuclear transport and processing phenotypes of 30 different point mutants generated by in vitro mutagenesis of a wild-type human tRNAimet gene. The effects of each nucleotide change on processing and transport were analyzed in X. laevis oocytes following nuclear microinjection of each mutant gene. Mutants exhibiting transport-defective behavior were further characterized by measuring transport kinetics of the purified mature tRNA. Our studies demonstrate that many mutations affect tRNAimet nuclear transport, although those with the most deleterious effects are clustered in the highly conserved D stem-loop and T stem-loop regions.

Animals↗
PubMed1984

Generation of long read-through transcripts in vivo and in vitro by deletion of 3' termination and processing sequences in the human tRNAimet gene.

The effects of 3' deletions of the coding and flanking regions of the human tRNAimet gene on its transcription and subsequent processing have been studied both in vitro and in vivo. We demonstrate that in the absence of the oligo T stop signal, polymerase III will read-through efficiently to the next available downstream stop signal. In mutations preserving the 3' terminal sequence of the coding region these read-through transcripts are efficiently processed, irrespective of their length and sequence by an endonucleolytic cleavage to yield both a mature tRNA and an intact trailer RNA. However, deletions involving the terminal regions up to +62 in the coding sequence produce an unprocessed co-transcript of tRNA and downstream sequences. Deletions further within the B promoter box abolish transcription. The use of these mutants as possible "portable" promoters is discussed.

Animals↗
PubMed1983

Two nonallelic tRNAiMet genes are located in the p23 leads to q12 region of human chromosome 6.

Two nonallelic human tRNAiMet genes were assigned to chromosome 6 by filter hybridization of DNA from human-rodent somatic cell hybrids by using probes containing unique sequences from the regions flanking each tRNAiMet gene. These unique sequence probes thus allowed each tRNAiMet gene to be analyzed individually in cell hybrids. Both tRNAiMet genes segregated in the hybrid cells with the chromosome 6 enzyme markers, soluble malic enzyme and the mitochondrial form of superoxide dismutase, and also with a karyotypically normal chromosome 6. By using hybrid clones containing translocations that divide chromosome 6 into five segments, both tRNAiMet genes were assigned to the p23 leads to q12 region. These results raise the possibility that other tRNAiMet genes may be syntenic with the two described in this study and illustrate the utility of using unique flanking sequences to identify members of a multigene family.

Alleles↗
PubMed1983

tRNA transport from the nucleus in a eukaryotic cell: carrier-mediated translocation process.

The mechanism by which a tRNA molecule is delivered from the nucleus of a cell to the cytoplasm has been studied in the Xenopus laevis oocyte utilizing nuclear microinjection and manual microdissection techniques. tRNA nuclear transport in this cell resembles a carrier-mediated translocation process rather than diffusion through a simple pore or channel. tRNA transport is saturable by tRNA, with a maximal rate measured to be about 190 X 10(7) molecules per min per nucleus (21 degrees C) in the mature oocyte. Competitive inhibition between two different tRNA species can be demonstrated, suggesting that many tRNA species share a common carrier system. tRNA nuclear transport is sharply dependent on temperature, with an optimal rate observed at 31 degrees C. A single G-to-U substitution at position 57 in the vertebrate tRNAMeti molecule reduces the transport rate of this tRNA by a factor of about 20, implicating this highly conserved region of the tRNA molecule (loop IV) as critical for recognition by the transport mechanism. On morphologic grounds I propose that ribosome-like components surrounding the nuclear pore may function as the tRNA translocation "motor." The tRNA nuclear transport mechanism represents a distinctly eukaryotic process and a site of potential control over cell growth and proliferation.

Animals↗
PubMed1982

Transcription and precursor processing of normal and mutant human tRNAiMet genes in a homologous cell-free system.

Two human tRNAiMet genes were previously cloned from a recombinant library of fetal liver DNA (Santos, T., and Zasloff, M. (1981) Cell 23, 699-709). One gene differed from the common vertebrate sequence by a G to T transversion at position 56, occupied exclusively by a purine in all prokaryotic and eukaryotic tRNAs. In this study, we show that although both tRNAiMet genes are transcribed in an in vitro system from KB cells, normal post-transcriptional processing of the mutant gene transcript is interrupted. While the primary transcript of the normal gene undergoes stepwise excision of its 5' and 3' terminal sequences, 5' preceding 3', only the 5' leader of the primary transcript of the mutant gene is excised, resulting in the accumulation of an intermediate containing an unprocessed 3' trailer. The results suggest that certain eukaryotic tRNA mutations may not appear in mature tRNA species due to the effects of the mutation on precursor processing.

Base Sequence↗