PubMed Health⌕ Search

Biomedical subjects

M Krabbe

Publications and source records attributed to M Krabbe.

14 recordsLinked to original sources
PubMed1999

Health and health behaviours among Swedish adolescents during a period of social change.

In Sweden there have been cutbacks in the welfare system and increasing unemployment during the 1990s. In what way have these external factors influenced health and behaviour among adolescents? The study describes health profiles and behaviours among students in three schools in Gothenburg, Sweden. Results are based on 2284 self-reports, representing 88% of available students in 7th and 9th grades with mean ages of 13.5 and 15.5 y, respectively. The study questionnaire was administered four times, in 1990, 1992, 1994 and 1996. The reported health and behaviours showed remarkable stability over the period. When the surveys from 1990 and 1992 were aggregated and compared with the surveys of 1994 and 1996 there was a small increase in psychosomatic symptoms, mental health symptoms and risk-taking behaviours. Despite the drastic social changes during the 1990s there was only a small change for the worse in reported health and behaviours. It is possible that the external changes had little impact on adolescent networks, or that the period was too short to have had much impact on health and behaviour.

Adolescent↗
PubMed1998

Conversion to bidirectional replication after unidirectional initiation from R1 plasmid origin integrated at oriC in Escherichia coli.

The cell division phenotypes of Escherichia coli with its chromosome replication driven by oriR (from plasmid R1) were examined by fluorescence microscopy and flow cytometry. Chromosome replication patterns in these strains were followed by marker frequency analyses. In one of the strains, the unidirectional oriR was integrated so that the replication fork moved clockwise from the oriC region, and bacterial growth and division were similar to those of the wild-type parent. The bacteria were able to convert the unidirectional initiation from oriR into bidirectional replication. The site for conversion of uni- to bidirectional replication seemed to be localized and could be mapped genetically within 6 min to the immediate right of the minimal oriC. Replication starting in the counterclockwise direction from the R1 replicon integrated at the same site in the opposite orientation could not be described as either bi- or unidirectional, as no single predominant origin could be discerned from the more or less flat marker frequency pattern. These strains also showed extensive filamentation, irregular nucleoid distribution and the presence of anucleate cells, indicative of segregation and division defects. Comparison among intR1 derivatives differing in the position of the integrated oriR relative to the chromosome origin suggested that the oriC sequence itself was dispensable for the conversion to bidirectionality. However, passage of the replication fork over the 6 min region to the right of oriC seemed important for the bidirectional replication pattern and normal cell division phenotype.

Cell Division↗
PubMed1998

Use of a two-color genetic screen to identify a domain of the global regulator Lrp that is specifically required for pap phase variation.

The global regulator Lrp plays a central role as both a repressor and an activator in Pap phase variation. Unlike most other members of the Lrp regulon such as ilvIH, activation of papBA transcription requires the coregulator PapI and is methylation dependent. We developed a two-color genetic screen to identify Lrp mutations that inhibit Pap phase variation but still activate ilvIH transcription, reasoning that such mutations might identify PapI binding or methylation-responsive domains. Amino acid substitutions in Lrp at position 126, 133, or 134 greatly reduced the rate of Pap switching from phase off to phase on but had much smaller effects on ilvIH transcription. In vitro analyses indicated that the T134A and E133G Lrp variants maintained affinities for pap and ilvIH DNAs similar to those of wild-type Lrp. In addition, both mutant Lrp's were as responsive to PapI as wild-type Lrp, evidenced by an increase in affinity for pap Lrp binding sites 4, 5, and 6. Thus, in vitro analyses did not reveal the step(s) in Pap phase variation where these Lrp mutants were inhibited. In vivo analyses showed that both the T134A and E133G Lrp mutants activated transcription of a phase-on-locked pap derivative containing a mutation in Lrp binding site 3. Further studies indicated that the T134A Lrp mutant was blocked in a step in Pap phase variation that does not involve PapI. Our data suggest that these mutant Lrp's are defective in a previously unidentified interaction required for the switch from the phase-off to the phase-on pap transcription state.

Amino Acid Sequence↗
PubMed1997

Inactivation of the replication-termination system affects the replication mode and causes unstable maintenance of plasmid R1.

Two so-called Ter sites, which bind the Escherichia coli Tus protein, are located near the replication origin of plasmid R1. Inactivation of the tus gene caused a large decrease in the stability of maintenance of the R1 mini-derivative pOU47 despite the presence of a functional partition system on the plasmid. Deletion of the right Ter site caused a drop in stability similar to that observed after inactivation of the tus gene. Substitution of 2bp required for Tus binding also caused unstable plasmid maintenance, whereas no effects on stability were observed when the left Ter site was deleted. Inactivation of the tus gene was coupled to an increased occurrence of multimeric plasmid forms as shown by gel electrophoresis of pOU47 DNA. Inactivation of the recA gene did not increase plasmid stability, suggesting that the multimerization was not mediated by RecA. Plasmid DNA was isolated from the tus strain carrying plasmid pOU47 and from a wild-type strain carrying pOU47 in which the right Ter site had been inactivated; in both cases, electron microscopy revealed the presence of multimers as well as rolling-circle structures with double-stranded tails. Thus, the right Ter site in plasmid R1 appears to stabilize the plasmid by preventing multimerization and shifts from theta to rolling-circle replication.

Bacterial Proteins↗
PubMed1993

DNA determinants of restriction. Bacteriophage T4 endonuclease II-dependent cleavage of plasmid DNA in vivo.

Endonuclease II of coliphage T4 is necessary for the in vivo restriction of plasmid DNA in phage-infected cells. Double-stranded restriction cleavage at 12 sites in pBR322 commenced before 10-min postinfection with T4 at 37 degrees C and proceeded more slowly in the presence of competing phage DNA than in its absence, utilizing the same sites in both cases; in a 200-base pair segment of the plasmid, single-stranded nicks also were frequent. The plasmid sites were cleaved with a speed that varied with the site, yielding frequencies of cleavage at different sites varying between 10 and 90%, at 50-min postinfection. All sites contained good matches to a consensus, 5'-GRCCGCNTYGC-3', most frequently cleaved around the variable central base pair, generating fragments with blunt ends or 1-2-base 5' overhangs. Using the frequency of cleavage to determine a weighted consensus, a larger sequence, 5'-CGRCCGCNTTGSYNGC-3', was identified. Thus, DNA sequence elements 3' to the cut site appear important for rapid cleavage. Several models describing the sequence-dependent structure of DNA suggest structural anomalies around the cleavage sites. The endonuclease II restriction system is most similar to type II systems, although it differs from known type II systems in several respects.

Amino Acid Sequence↗
PubMed1992

Mapping of the in vivo start site for leading strand DNA synthesis in plasmid R1.

We have previously constructed Escherichia coli strains in which an R1 plasmid is integrated into the origin of chromosome replication, oriC. In such intR1 strains, oriC is inactive and initiation of chromosome replication instead takes place at the integrated R1 origin. Due to the large size of the chromosome, replication intermediates generated at the R1 origin in these strains are considerably more long-lived than those in unintegrated R1 plasmids. We have taken advantage of this and performed primer extensions on total DNA isolated from intR1 strains, and mapped the free 5' DNA ends that were generated as replication intermediates during R1 replication in vivo. The sensitivity of the mapping was considerably improved by the use of a repeated primer extension method (RPE). The free DNA ends were assumed to represent normal in vivo start sites for leading strand DNA synthesis in plasmid R1. The ends were mapped to a short region approximately 380 bp away from the R1 minimal origin, and the positions agreed well with previous in vitro mappings. The same start positions were also utilized in the absence of the DnaA protein, indicating that DnaA is not required for determination of the position at which DNA synthesis starts during initiation of replication at the R1 origin.

Bacterial Proteins↗
PubMed1991

In vivo restriction. Sequence and structure of endonuclease II-dependent cleavage sites in bacteriophage T4 DNA.

Endonuclease II of bacteriophage T4 is required for in vivo restriction of cytosine-containing DNA from its host, Escherichia coli, (as well as from phage mutants lacking cytosine modification), normally the first step in the reutilization of host DNA nucleotides for synthesis of phage DNA in infected cells. The phage cytosine-DNA is fragmented incompletely to yield genetically defined fragments. This restriction is different from that of type I, II, or III restriction enzymes. We have located seven major endonuclease II-dependent restriction sites in the T4 genome, of which three were analyzed in detail; in addition, abundant sites were cleaved in less than or equal to 5% of all molecules. Sites I, II, and III shared the sequence 5'-CCGNNTTGGC-3' and were cleaved in about 25% (I and III) and 65% (II) of all molecules, predominantly staggered around the first or second of the central unspecified base pairs to yield fragments with one 5' base. The less frequently cleaved sites I and III deviated from site II in predicted helical structure when viewed from the consensus strand, and in sequence when viewed from the opposite strand. Thus, interaction with a particular helical structure as well as recognition of the bases in DNA appears important for efficient cleavage.

Base Sequence↗
PubMed1991

Absenteeism because of illness at daycare centers and in three-family systems.

Absenteeism because of illness was recorded for 346 children and 98 staff members at eight daycare centers in Gothenburg during a nine-month period between October 1987 and June 1988. A comparison was made with a similar, nationwide study, carried out in 1977 by the Swedish Central Bureau of Statistics. This comparison demonstrated that the absence of children and employees from daycare centers for health reasons was of the same proportion in the present study as that reported a decade earlier. Absenteeism because of illness among the 346 children at the daycare centers was also compared with absenteeism among 49 children in 14 groups run according to the three-family system (three to six children/group). It was found that absenteeism was at least twice as frequent among children at daycare centers than among those in the three-family system.

Absenteeism↗