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O L Miller

Publications and source records attributed to O L Miller.

At least 37 records · Page 2Linked to original sources
PubMed1988

Visualization of Drosophila melanogaster chorion genes undergoing amplification.

We visualized by electron microscopy the preferential amplification of Drosophila chorion genes in late-stage follicle cells. Chromatin spreads revealed large clusters of actively transcribed genes of the appropriate size, spacing, and orientation for chorion genes that were expressed with the correct temporal specificity. Occasionally the active genes were observed within or contiguous with intact replicons and replication forks. In every case, our micrographs are consistent with the hypothesis that the central region of each chorion domain contains a replication origin(s) used during the amplification event. In one case, a small replication bubble was observed precisely at the site of the essential region of the X chromosome amplification control element. The micrographs also suggest that forks at either end of a replicon frequently progress very different distances, presumably due to different times in initiation or different rates of movement. It appears that all chorion genes (even those coding for minor proteins) are transcribed in a "fully on" condition, albeit for varied durations, and that if replication fork passage does inactivate a promoter, it does so very transiently. Furthermore, a DNA segment containing one active gene is likely to have an additional active gene(s). Surprisingly, during the time frame of expected maximum activity, approximately half of the chorion sequences appear transcriptionally inactive.

Animals↗
PubMed1986

Two Drosophila chorion genes terminate transcription in discrete regions near their poly(A) sites.

We have examined transcription termination of two closely linked Drosophila melanogaster chorion genes, s36-1 and s38-1, using the electron microscope. Our method is unusual and is independent of in vitro nuclear run-on transcription. By measuring transcription unit lengths in chromatin spreads, we can localize efficient termination sites to a region of approximately 210 bp for s36-1 and approximately 365 bp for s38-1. The center of this region is approximately 105 nucleotides downstream of the poly(A) site for the s36-1 gene, and approximately 400 nucleotides downstream for the s38-1 gene. Thus, these two Drosophila chorion genes terminate more closely to their poly(A) addition sites and in a shorter region than many other polyadenylated genes examined to date.

Animals↗
PubMed1986

Electron microscopic study of Saccharomyces cerevisiae rDNA chromatin replication.

An electron microscopic study was made of the replication of rDNA chromatin of Saccharomyces cerevisiae. Two different methods were used to synchronize cells. cdc7-1 cells were raised to a restrictive temperature, whereas A364a cells were blocked with mating factor. Replication bubbles typically opened in the nontranscribed spacers of rDNA repeats in both cell types. The mean position of the center of these bubbles corresponds closely to a position where an autonomously replicating sequence previously has been mapped in an rDNA repeat. Clusters of replication bubbles containing up to four bubbles spaced one to three genes apart were seen opening in early S phase.

Chromatin↗
PubMed1985

RNP particles at splice junction sequences on Drosophila chorion transcripts.

HnRNP particles are located at specific sites on nascent transcripts when chromatin is spread for electron microscopic visualization. To determine if the sequences bound by the particles play a role in RNA processing, we have correlated the nascent transcript morphology of Drosophila chorion s36-1 and s38-1 genes with their nucleotide sequences. We find that RNP particles about 25 nm in diameter are at the splice junctions of the introns in these two transcripts. On the more mature chorion transcripts, a single larger (40 nm) particle is occasionally seen in the same vicinity, which probably results from the coalescence of the two smaller particles. This RNP structure may be involved in bringing splice junctions into close proximity and in maintaining this proximity during the bipartite splicing intermediate stage.

Animals↗
PubMed1985

Electron microscopic visualization of trp operon expression in Salmonella typhimurium.

Transcriptional activity of plasmids carrying wild-type and mutant trp operons was visualized in cell lysates of Salmonella typhimurium. Plasmid and transcription-unit sizes varied with the size of the cloned operon. Following 3-(3-indolyl)acrylic acid derepression, all operons of a particular type exhibited the same high level of transcriptional activity. An estimated 11-14 transcripts must be initiated each minute to maintain the 190-base-pair spacing of RNA polymerases observed on the promoter-proximal half of the wild-type trp operon. A decline in RNA polymerase density was observed on promoter-distal portions of cloned trp operons, which may be attributable to premature transcription termination accompanying translation inhibition due to indolylacrylic acid's interference with normal tryptophanyl-tRNA synthetase activity.

Chromosome Deletion↗
PubMed1984

The rare transcripts of interrupted rRNA genes in Drosophila melanogaster are processed or degraded during synthesis.

About 50% of the ribosomal transcription units in females of the bobbed 8 mutant of Drosophila melanogaster contain an intervening sequence of 5 kb in the 28S region of the gene. We analysed the transcription of ribosomal genes in this mutant using electron microscopy and found that the majority of the active ribosomal transcription units in larval fat bodies and guts are not long enough to contain the 5-kb intervening sequence; only approximately 1% of active transcription units have a length consistent with the presence of the 5-kb intervening sequence. Transcription units of this length show an interrupted gradient of nascent RNA fibril lengths indicative of processing or degradation during transcription. The position of the discontinuity in RNA length coincides with the position of the intervening sequence. This observation suggests that even though RNA polymerase may infrequently transcribe an entire interrupted gene, the process does not result in a full-length RNA.

Animals↗
PubMed1984

Gastric stapling for morbid obesity: gastrointestinal response in a rat model.

The adaptive response of the gastrointestinal tract to gastric stapling was studied in a Zucker (fafa) genetically obese rat model. The effects of gastric stapling in rats with a Roux-en-Y gastrojejunostomy were compared to Roux-en-Y and intact controls. Rats (225 to 275 g) were divided into three groups: group I (GI), Roux-en-Y, stapled, ad libitum fed; group II, Roux-en-Y, unstapled; and group III, intact (laparotomy only). Groups II and III were further subdivided into group IIA (GIIA) and group IIIA (GIIIA), pair-fed to GI; and group IIB (GIIB) and Group IIIB (GIIIB), fed ad libitum. All rats were fed a diet of liquid rat formula and rat food (50:50 cal ratio). After 2 wk rats were killed and the liver, pancreas, and stomach removed, weighed, and tissue taken for histology. The intestine was divided into three segments corresponding to the excluded segment (1, duodenum), transposed segment (2, jejunum), and ileal segment (3), with tissue taken for histology. Liver lipid, pancreatic amylase, serum amylase and gastrin, and intestinal mucosal protein and DNA were measured. Weight gain, g/14 days, was: GI, 24.1 +/- 7.8; GIIA, 17.0 +/- 2.0; GIIB, 42.6 +/- 4.8; GIIIA, 17.6 +/- 4.7; GIIIB, 54.6 +/- 8.9. All rats were in positive N balance. Liver weight and lipid were similar in all groups. Pancreatic mass was significantly increased in all Roux-en-Y animals, while amylase activity per g tissue was significantly less than in intact animals. Stapled rats had atrophy of the glandular portion of the stomach, decreased stomach mucosal weight, and lower serum gastrin concentration compared with all other rats (p less than 0.01). In stapled rats, segment weight and mucosal weight were lower in the excluded segment, and higher in the transposed segment, compared to all other rats. Tissue pathology was found only in stapled rats: gastric atrophy, focal fibrosis of gastric wall, peritonitis, minimal to mild multifocal hepatitis, and mild periductal fibrosis of the pancreas. There are significant early adaptive and pathological changes after gastric stapling in the rat.

Adaptation, Physiological↗
PubMed1984

Some ultrastructural aspects of genetic activity in eukaryotes.

A brief overview is given of the types of information that have been obtained by chromatin spreading methods regarding the ultrastructure and regulation of genetic units. The examples used are: ribosomal RNA genes of the spotted newt; the silk fibroin gene of Bombyx mori; chorion gene amplification in Drosophila melanogaster; RNA synthesis patterns during early embryogenesis of D. melanogaster; regulation of transcription on homologous non-ribosomal transcription units of D. melanogaster; specific nascent transcript cleavage in insects; and nascent polypeptides on insect polyribosomes. The conclusion is drawn that further innovations will be required before significant advances in the use of chromatin spreading techniques to study ultrastructural aspects of genetic activity can occur.

Animals↗
PubMed1983

Polysome structure in sea urchin eggs and embryos: an electron microscopic analysis.

Modified chromatin-spreading techniques have been used to prepare reproducible spreads of polysomes for EM visualization. We have analyzed polysomes of sea urchin (Lytechinus pictus) eggs and embryos to elucidate some of the events which occur during the burst of protein synthetic activity following fertilization. We have confirmed that the rise in protein synthesis after fertilization is concomitant with the recruitment of messenger RNA molecules into polysomes. The presence of ribosome-free tails is a structural feature of polysomes in which the mRNA is being translated for the first time. This structural marker has allowed us to derive an elongation rate of 1.5-1.8 amino acids/sec and a transit time of 5 min for the average-sized polysome in L. pictus embryos at 16 degrees C. We have also observed a difference between the structure and the average size of polysomes in the egg and embryo. Egg polysomes are longer (average size = 11.96 ribosomes, n = 671) than 1-hr embryo polysomes (average size = 7.14 ribosomes, n = 863) and 10% of the egg polysomes contain visible gaps while less than 1% of the 1-hr embryo polysomes contain internal ribosome-free regions. We speculate that such differences reflect the lower translation efficiency of the relatively dormant egg cell.

Age Factors↗
PubMed1983

Novel amplification and transcriptional activity of chorion genes in Drosophila melanogaster follicle cells.

Single-copy chorion genes coding for egg shell proteins are amplified in the follicle cells of Drosophila melanogaster egg chambers. Chromatin spreads of appropriately staged follicle cells reveal complex, multi-forked chromosomal structures in which one chromatin strand branches into two, which themselves branch out, and so on. In one micrograph, 13 strands originating from a single strand were observed. These structures can account for the maximal amplification occurring in the center of the domain, where the major chorion genes are located, and the decreasing amplification of flanking sequences to both sides. The amplification, high transcriptional rate, stage-specific expression, and correlation with known molecular sizes have allowed the putative identification of the single-copy, major chorion genes on the X chromosome and on chromosome III.

Animals↗
PubMed1982

Electron microscopic visualization of a discrete class of giant translation units in salivary gland cells of Chironomus tentans.

Lysates were made of whole salivary glands from Chironomus tentans and electron microscopic spreads prepared according to Miller and Beatty (1969). The sedimented material consisted mainly of ribosomes, most of which were present in giant polysomes which showed gradients of material protruding laterally from the ribosomes, interpreted as nascent polypeptide chains. Each giant polysome contained one such gradient. On the basis of the presence of a small group of terminal ribosomes without nascent chains at the 3' end, 19 apparently complete polysomes were selected, representing a discrete class of polysomes containing between 66 and 92 ribosomes (79 +/- 7, m +/- s.d.). Arguments are presented that they constitute the translation units for giant secretory proteins coded by RNA from the large Balbiani rings, BR1 and BR2.

Journal Article↗
PubMed1981

Correlation of hnRNP structure and nascent transcript cleavage.

Using electron microscopy of spread chromatin, we have observed nonnucleolar transcription units from Drosophila melanogaster and Calliphora erythrocephala that display specific cleavage of nascent transcripts. We have quantitatively analyzed 20 of these relatively long transcription units. The primary RNP structure of homologous transcripts is nonrandom with respect to both RNA sequence and the cleavage event. In general, released RNA fragments have a smooth fibrillar RNP morphology (approximately 50 A wide) and retained segments have a thicker particulate morphology (approximately 250 A diameter). A characteristic secondary structure formation also accompanies cleavage--that is, RNP fibril loops form by association of noncontiguous transcript sequences that correspond to the terminal regions of the segment to be released. RNP particles form at the loop base sequences prior to their association and apparently coalesce upon loop formation. These loops, and thus the released segments, range in length from 1 and 25 kb on the examples we have analyzed. Cleavage of nascent hnRNA transcripts appears to be a fairly common event in these organisms and occurs within 0.3-3 min after transcription of the cleavage site.

Animals↗
PubMed1980

Ribonucleoprotein structure in nascent hnRNA is nonrandom and sequence-dependent.

We have studied the ribonucleoprotein morphology of nascent hnRNA using chromatin spreading methods. This approach allows visualization of multiple transcripts of the same DNA sequence. Thus the RNP structure of hnRNA molecules with the same nucleotide sequence can be compared. We find that RNP particles averaging 240 A in diameter occur on the majority of hnRNA transcription units, but that RNA fibrils are generally not completely covered with particles. Furthermore, the RNP particle location is nonrandom for the transcripts of a given gene. Particle number and arrangement on RNP fibrils vary from one transcription unit to the next, and are not obviously related to transcription unit size or activity. Analysis of particle location with respect to the 5' RNA terminus allows RNP particle localization to homologous sequences of less than 500 ribonucleotides on the different fibrils of a single transcription unit. RNP particles assemble very soon after synthesis of the particular sequence. Sites of particle formation are distinct from sites of double-stranded hairpin loops on the RNA fibrils. A differential, or differentially stable, RNP structure with respect to RNA sequence may bear on mechanisms of specific hnRNA processing.

Animals↗
PubMed1979

Post-replicative nonribosomal transcription units in D. melanogaster embryos.

We have analyzed transcription units from D. melanogaster embryos in which most cells were in either the late S or the G2 phase of a synchronous cell cycle. Much of the chromatin of these embryos was observed in the form of parallel strands which appear to be newly replicated sister chromatids (McKnight and Miller, 1977). Lateral ribonucleoprotein (RNP) fibers were commonly observed attached to chromatin strands and are believed to be nascent transcripts. Very similar lateral fiber arrays were found on sister chromatid strands. Such paired, post-replicative RNP fiber arrays offer a unique opportunity to compare the transcription patterns on two copies of the same transcription unit. Analyses of paired transcription units yield the following conclusions. Transcription initiation and termination sites are the same for both copies of each transcription unit. Each transcription unit has a characteristic and constant RNP fiber frequency, and the fiber frequency is identical for both copies of the transcription unit. Active transcription units can have internal, fiber-free gaps which may result from interruptions in initiation of transcription. Transcription units differing in polarity and fiber frequency can occur in immediate juxtaposition. The relevance of these findings to eucaryotic transcriptional control mechanisms are discussed.

Animals↗
PubMed1979

Coronary arterial bypass operations without antibiotic coverage.

In this study, six of 693 consecutive patients in 29 months who underwent only myocardial revascularization, without prophylactic systemic therapy with antibiotics, experienced infection of a clean wound. This incidence of infection (0.86 percent) in such patients is the lowest reported in the literature. Prevention of infection of clean mediastinal wounds in patients undergoing only myocardial revascularization is related to preoperative preparation of the skin and local antibiotic irrigation of the wound, rather than to prophylactic systemic therapy with antibiotics.

Administration, Topical↗