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Biomedical subjects

D Carroll

Publications and source records attributed to D Carroll.

At least 217 records · Page 12Linked to original sources
PubMed1983

Tandemly repeated DNA sequences from Xenopus laevis. II. Dispersed clusters of a 388 base-pair repeating unit.

A repetitive DNA sequence family from Xenopus laevis that has an unusual genomic organization has been identified. It has been shown by blot-hybridization that this sequence occurs in clusters containing variable numbers of the 388 base-pair repeating unit. There are approximately 500 such clusters in the genome, and each cluster has common flanking sequences. The number of tandem 388 base-pair repeats per cluster ranges from one to at least 15, with a mean of seven. Homologous sequences were found in two related species, Xenopus borealis and Xenopus mulleri, where the size of the repeating units and their genomic arrangement are very similar to those in X. laevis. The complete nucleotide sequence of a cloned representative 388 base-pair repeating unit showed no short internal repeats and no long reading frames. By blot-hybridization, no evidence of transcripts of this sequence was found in total RNA from X. laevis liver, embryos or oocytes.

Animals↗
PubMed1983

Genetic recombination of bacteriophage lambda DNAs in Xenopus oocytes.

Pairs of genetically marked bacteriophage lambda DNAs have been injected into Xenopus laevis oocyte nuclei. After suitable incubation, DNA was recovered and packaged into phage particles in vitro. When these were plated onto a selective host, phage recombinant for parental markers were observed. Recombination was dependent on both parents being present in the same oocyte nucleus and was roughly proportional to the physical separation of the markers. Thus, the oocytes appear to contain the machinery necessary for performing typical genetic recombination. This system offers a great deal of scope and flexibility for future studies of recombination mechanisms at the molecular level in vertebrates.

Animals↗
PubMed1983

Regular arrangement of nucleosomes on 5S rRNA genes in Xenopus laevis.

The chromatin structure of the oocyte-type 5S RNA genes in Xenopus laevis was investigated. Blot hybridization analysis of DNA from micrococcal nuclease digests of erythrocyte nuclei showed that 5S DNA has the same average nucleosome repeat length, 192 +/- 4 base pairs, as two Xenopus satellite DNAs and bulk erythrocyte chromatin. The positions of nuclease-sensitive regions in the 5S DNA repeats of purified DNA and chromatin from erythrocytes were mapped by using an indirect end-labeling technique. Although most of the sites cleaved in purified DNA were also cleaved in chromatin, the patterns of intensities were strikingly different in the two cases. In 5S chromatin, three nuclease-sensitive regions were spaced approximately a nucleosome length apart, suggesting a single, regular arrangement of nucleosomes on most of the 5S DNA repeats. The observed nucleosome locations are discussed with respect to nucleotide sequences known to be important for expression of 5S RNA. Because the preferred locations appear to be reestablished in each repeating unit, despite spacer length heterogeneity, we suggest that the regular chromatin structure reflects the presence of a sequence-specific DNA-binding component on inactive 5S RNA genes.

Animals↗
PubMed1983

Role of defective simian virus 40 genomes in establishment and maintenance of persistently infected primate cell lines.

Studies are reported of persistent simian virus 40 (SV40) infections of fully permissive monkey (TC-7 and BSC-1) and human (A172) cell lines, with emphasis on the role of viral defectives in establishment and maintenance of persistence. The presence of defectives prevented complete cell killing and allowed the establishment of persistently infected cultures. Hirt supernate DNAs from these cultures showed the continuing presence of defective genomes. Restriction enzyme analysis demonstrated that altered defective genomes evolved during passage of the carrier cultures, but that they always reflected structures of the genomes used to established the cultures. There was some host cell specificity in the effectiveness of establishment of persistence, e.g., TC-7-derived defectives were more effective in preventing killing of TC-7 than of BSC-1 or A172 cells. Persistent infections of TC-7 cells could also be established in the absence of defectives, but in the presence of neutralizing anti-SV40 antiserum. In fact, defectives were eliminated from carrier cultures established in the presence of antiserum. When antiserum was withdrawn, the wild-type SV40 grew and destroyed the cells. Antiserum maintains a low level of infection by neutralizing viruses outside the cells, so that many cells do not become infected. Defectives are eliminated because spread of infection is effectively at very low multiplicity. Carrier cultures that are established and maintained by defectives result from intracellular interference by the defectives with the normal development of wild-type virus.

Animals↗
PubMed1982

Isolation and characterization of defective simian virus 40 genomes which complement for infectivity.

A new variant of simian virus 40 (EL SV40), containing the complete viral DNA separated into two molecules, was isolated. One DNA species contains nearly all of the early (E) SV40 sequences, and the other DNA contains nearly all of the late (L) viral sequences. Each genome was encircled by reiterated viral origins and termini and migrated in agarose gels as covalently closed supercoiled circles. EL SV40 or its progenitor appears to have been generated in human A172 glioblastoma cells, as defective interfering genomes during acute lytic infections, but was selected during the establishment of persistently infected (PI) green monkey cells (TC-7). PI TC-7/SV40 cells contained EL SV40 as the predominant SV40 species. EL SV40 propagated efficiently and rapidly in BSC-1, another line of green monkey cells, where it also formed plaques. EL SV40 stocks generated in BSC-1 cells were shown to be free of wild-type SV40 by a number of criteria. E and L SV40 genomes were also cloned in the bacterial plasmid pBR322. When transfected into BSC-1 cell monolayers, only the combination of E and L genomes produced a lytic infection, followed by the synthesis of EL SV40. However, transfection with E SV40 DNA alone did produce T-antigen, although at reduced frequency.

Animals↗
PubMed1981

Effects of heart-rate biofeedback and false feedback on reactions to stressful stimulation.

Three groups of 10 subjects were exposed to intermittent bursts of loud noise. Two groups attempted bi-directional cardiac control immediately prior to the noise bursts, one with the aid of continuous heart-rate biofeedback and one without. The third group did not attempt heart-rate control but instead received false feedback that heart rate was either increasing or decreasing prior to the noise bursts. Only the biofeedback-assisted group demonstrated reliably different cardiac changes during attempted heart-rate increase and decrease. The heart rates of the false-feedback subjects were unaffected by the direction of change signalled by the biofeedback display. However, a significant differential effect on subjects' ratings of the noise bursts, in terms of loudness and unpleasantness, was apparent only in the false-feedback group. Skin conductance responses showed no such effect in any of the three groups. The results are most readily accounted for in terms of attribution theory.

Adolescent↗
PubMed1980

Bacteriophage lambda cloning vehicles for studies of genetic recombination.

A pair of bacteriophage lambda cloning vehicles has been constructed for use in studies of genetic recombination. These phages, lambda rva and lambda rvb, have the following properties: (1) Each vector has a single HindIII site in the immunity region, at which segments of DNA can be inserted. (2) These HindIII sites are flanked by selectable markers with the following phenotypes: Spi+/- (Fec+/-) to the left, and imm lambda or imm434 to the right. (3) There is essentially no sequence homology between the two phages in this region, so recombination of the markers at reasonable frequency depends on the presence of homologous inserts at the HindIII sites. As a consequence, recovered recombinants must have resulted from a crossover event within the insert DNA. Restriction enzyme maps of the vectors have been determined. Variants of the original vectors have been isolated which permit separate examination of the viral (Red) and bacterial (Rec) generalized recombination mechanisms, and which provide a standard interval to which frequencies of recombination in cloned DNAs can be compared.

Bacteriophage lambda↗
PubMed1980

Recombination of a eukaryotic DNA in bacteria.

Single, 824 bp repeating units of xenopus laevis oocyte-type 5S DNA were inserted into the recombination vectors, lambda rva and lambda rvb. When the inserts had the same orientation with respect to the lambda chromosomes. Spi- imm434 recombinants were recovered by selection on a P2, lambda double lysogenic host. Because of the structure of the vectors, the crossover point in each recombinant must lie completely within the 5S DNA insert. The physical characteristics of these recombinants were determined by examination of restriction enzyme digests. By use of RecA mutant hosts and the Red- vector, lambda rvc, recombination frequencies were measured separately for the bacterial and phage systems. Some of the recombination events resulted in 5S DNA inserts of altered length due to unequal crossovers within repeated sequences in the 5S DNA spacer. The occurrence of just such events in frog 5S DNA had been predicted, based on the structure of 5S DNA and evolutionary considerations.

Animals↗