Search PubMed⌕ Search

Biomedical subjects

J G Gall

Publications and source records attributed to J G Gall.

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

5S ribosomal RNA genes of the newt Notophthalmus viridescens.

The genes which code for the 5S ribosomal RNA in the newt, Notophthalmus viridescens have been cloned and analyzed. Two types of repeating unit were detected: a major type consisting of a 120 bp coding region with a 111 bp spacer, and a minor type composed of a coding region, a pseudogene, and a 113 bp spacer. The pseudogene is a 36 bp segment which corresponds to the 3' terminal third of the 5S RNA gene, and is situated immediately 3' to the gene, being separated from it by 2 bp. Two recombinant plasmids were obtained in which the major and minor units were arranged in an interspersed pattern.

Animals↗
PubMed1981

Characterization of a cloned histone gene cluster of the newt Notophthalamus viridescens.

We report the cloning and characterization of a histone gene cluster of the newt Notophthalamus viridescens. Fragments containing newt histone genes were identified in whole genome Southern blots; these fragments were cloned into a bacteriophage lambda cloning vector constructed for this purpose. The positions of most of the histone genes were determined by hybridizing subcloned sea urchin histone genes to digests of the cloned newt gene cluster. The position of each gene was verified, and its polarity determined by sequencing a portion of each. The order of the genes in the cloned segment is H1-H3-H2B-H2A-H4, with each of the genes but H2B being transcribed in the same direction. Subcloned segments of the histone gene repeat were used to determine the size of each newt oocyte histone mRNA.

Amino Acid Sequence↗
PubMed1981

In vitro RNA synthesis in oocyte nuclei of the newt Notophthalmus.

An incubation medium is described which supports RNA synthesis in isolated oocyte nuclei of the newt Notophthalmus, and which permits subsequent autoradiographic examination of the lampbrush chromosomes and nucleoli. By using different concentrations of alpha-amanitin we distinguish RNA synthesis due to RNA polymerases I, II and III. All RNA synthesis on loops is inhibited by 0.5 microgram/ml of alpha-amanitin and is therefore due to polymerase II. Polymerase III is responsible for RNA synthesis at a small number of discrete sites in condensed chromatin. These include the centromere bars of three of four chromosomes, which probably represent 5S RNA synthesis, as well as 15-20 lesser sites scattered elsewhere. Polymerase I activity is confined to the nucleoli.

Amanitins↗
PubMed1981

Histone genes are located at the sphere loci of newt lampbrush chromosomes.

In situ hybridization experiments on mitotic and lampbrush chromosomes show that histone genes and an associated 222 bp repeated sequence, satellite 1, are located at or near the sphere loci of chromosomes 2 and 6 of the newt Notophthalmus viridescens. During the lampbrush chromosome stage, transcripts of the histone genes and of satellite 1 occur on loops associated with the spheres. Histones genes are located at sites on the mitotic chromosomes of Triturus cristatus and T. alpestris which are consistent with the known positions of spheres on their lampbrush chromosomes.

Animals↗
PubMed1981

Histone gene clusters of the newt notophthalmus are separated by long tracts of satellite DNA.

The genomic organization of the histone genes of the newt Notophthalmus viridescens is described. Genes for the five proteins are clustered on a 9.0 kb segment of cloned DNA which is part of a homogeneous family of sequences containing 600--800 members per haploid genome. The 9.0 kb histone gene clusters are not adjacent in the genome, but are separated from neighboring clusters by up to 50 kb or more of cluster spacer sequences; some or all of these spacer sequences are members of a predominantly centromeric satellite DNA with a 2235 bp repeating unit.

Animals↗
PubMed1981

Transcripts from both strands of a satellite DNA occur on lampbrush chromosome loops of the newt Notophthalmus.

We have isolated genomic DNA clones from the newt Notophthalmus which contain one or more copies of a 222 bp tandemly repeated sequence (satellite 1). Satellite 1 occurs in the pericentromeric heterochromatin of all chromosomes and at the sphere loci of chromosomes 2 and 6. Lampbrush chromosome loops associated with the spheres contain transcripts of satellite 1, as shown by in situ hybridization. The matrix on these loops consists of multiple thin--thick transcription units, most but not all of which have the same polarity within a given loop. By in situ hybridization with single-stranded probes we show that transcription units of opposite morphological polarity contain transcripts of opposite strands of satellite 1. Satellite 1 occurs as the spacer between clusters of histone genes. We postulate that transcription initiates at a histone gene promoter, fails to terminate at the end of the gene and continues without interruption into the adjacent satellite DNA. In this way, long transcripts are produced which contain both histone and satellite 1 sequences. A general failure of termination signals might explain the unusually long transcripts of lampbrush chromosomes.

Animals↗
PubMed1981

In vitro transcription of cloned 5S RNA genes of the newt Notophthalmus.

Recombinant plasmids that carried genes coding for 5S ribosomal RNA of the newt, Notophthalmus viridescens, were transcribed in vitro with extracts of Xenopus laevis oocyte nuclei. Plasmids containing multiple repeats of the 5S gene and spacer directed accurate transcription of 5S RNA (120 bases). Individual repeat units were recloned by inserting Sau 3A restriction fragments into the Bam HI site of plasmid pBR322. Because each repeat was cut by the enzyme within the coding region, the inserts had incomplete coding regions at their ends and spacer sequences in the middle. The DNA of these subclones directed synthesis of a 5S-size RNA that contained both plasmid and 5S RNA sequences. Transcription initiated in the vector, proceeded through the gene segment coding for nucleotides 41-120, and terminated at the end of the gene. The initiation of in vitro transcription required neither the original 5' flanking sequences of the spacer nor the first third of the gene. We conclude that intragenic DNA sequences control the initiation of transcription. Other subclones that include pseudogenes gave rise to some transcripts 156 nucleotides long. These long transcripts represented continuation of transcription through the 36-base-pair pseudogene that is located immediately downstream from the 5S gene. However, most transcripts of these subclones terminated at the end of the normal gene before the beginning of the pseudogene. It is probable that a run of four or more Ts serves as part of the termination signal.

Animals↗
PubMed1980

Organization of ribosomal genes in Paramecium tetraurelia.

The macronuclear ribosomal DNA (rDNA) of the ciliated protozoan Paramecium tetraurelia (stock 51) was analyzed by digestion with restriction endonucleases. The fragments which contained ribosomal RNA (rRNA) coding sequences and spacer sequences were identified. The spacer sequences exhibited some heterogeneity in size. The genes coding for 5.8S RNA, but not for 5S RNA, are linked to the 17S and 25S rRNA genes. Complementary RNA, synthesized from rDNA of stock 51, was hybridized with restriction digests of whole cell DNA from six other allopatric stocks of this species. The restriction patterns of the rDNA from these seven stocks were, in general, very similar, and the sizes of the coding sequences were identical in all seven stocks. Only the restriction pattern of rDNA from stock 127 differed significantly from that of stock 51. The rDNA from stock 127 was isolated and characterized, and with the exception of the restriction pattern of its spacer, it resembled the rDNA from stock 51. It is concluded that the rDNA repeat in Paramecium, including the spacer, has, in general, been conserved during the course of evolution. It is suggested that in some species, even in the absence of genetic exchange among geographically separated populations, selection pressure may act to conserve spacers of tandemly repeated rDNA. The conservation may be related to the number of rDNA copies in the germinal nucleus.

Animals↗
PubMed1980

Structure of mitochondrial DNA from Paramecium tetraurelia.

Mitochondrial DNA (mtDNA) from endosymbiote-free stocks of Paramecium tetraurelia was isolated by 2 procedures. The buoyant density of the mtDNA in neutral CsCl was 1.702 gm/cm3, a value consistent with the melting temperature of the mtDNA. Only linear molecules were observed by electron microscopy. These molecules were homogeneous in size with a monomer molecular weight of 25.6 x 10(6) daltons. The size of the mtDNA determined after digestion with the restriction endonucleases EcoRI or Hind III agreed with the value obtained by electron microscopy. These studies also revealed that the digestion pattern of mtDNA from stock 172 differed from that of other 3 stocks (51, 127, 203) examined. Some mtDNA molecules exhibited snapback reassociation following denaturation.

Animals↗
PubMed1979

An intervening sequence in the gene coding for 25S ribosomal RNA of Tetrahymena pigmentosa.

An intervening sequence of approximately 400 bp has been discovered in the 25S ribosomal RNA gene (rDNA) from macronuclei of Tetrahymena pigmentosa strain 6UM. Another strain, 8ALP, lacks the intervening sequence in its macronuclear rDNA. The presence of the intervening sequence was first suggested by a comparison of the restriction endonuclease maps of the rDNA from each strain. A region which differed in size between the two strains was shown to lie within the region coding for 25S ribosomal RNA by hybridization of the restriction fragments to labeled 25S rRNA. Direct visual evidence for the existence of the intervening sequence in 6UM and its absence from 8ALP was obtained by electron microscopy of R loop hybrids formed between the rDNA and 25S rRNA. The size and position of the intervening sequence within the gene were further defined by detailed restriction analyses of cloned fragments of the rDNA from each strain. The rDNA within the macronucleus of each of these strains is homogeneous, and thus the intervening sequence in the rDNA of strain 6UM must not interfere with transcription of the gene. Furthermore, the presence or absence of the intervening sequence has no obvious functional importance, since both strains can survive and grow equally well.

Base Sequence↗
PubMed1978

Free ribosomal RNA genes in Paramecium are tandemly repeated.

The genes coding for 17S and 25S rRNA in Paramecium tetraurealia were isolated. The macronuclear ribosomal DNA (rDNA) exists as relatively small, extrachromosomal molecules with both linear and circular forms. Electron microscopy and restriction endonuclease analysis revealed that the rDNA is arranged as tandem repeats with an average repeat size of 5.5 X 10(6) daltons. Some heterogeneity of repeat lengths was found both by electron microscopy and by restriction enzyme analysis. The rDNA does not snap back after denaturation. This study provides additional evidence that extrachromosomal rDNA may be a common feature among lower eukaryotes. However, in contrast to several other cases, the rDNA of Paramecium is not palindromic, but occurs as tandem repeats as in higher eukaryotes.

Animals↗
PubMed1977

The replication of ribosomal DNA in the macronucleus of Tetrahymena.

The replication of extrachromosomal rDNA molecules from the macronucleus of Tetrahymena was studied by electron microscopy. Replication begins in the center of the palindromic molecule and proceeds by means of bidirectional fork movement toward the free ends of the molecule.

Bromodeoxyuridine↗
PubMed1977

A single integrated gene for ribosomal RNA in a eucaryote, Tetrahymena pyriformis.

The macronucleus of the protozoan, Tetrahymena, is known to contain multiple rRNA genes which are not linked to the chromosomes. Here we present evidence that the germinal micronucleus of this organism contains a single gene for rRNA integrated into the chromosomal DNA. Unlike the extrachromosomal copies of the macronucleus, which are composed of a pair of reversely repeated sequences (a palindrome), the integrated copy of rDNA is nonrepetitive or half the size of the extrachromosomal rDNA. Furthermore, we have failed to detect such an integrated copy of rDNA in the macronucleus. The implications of these observations for the amplification and evolution of rDNA are discussed.

Animals↗