Search PubMed⌕ Search

Biomedical subjects

M J Stark

Publications and source records attributed to M J Stark.

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

A psychoeducational approach to methadone maintenance treatment.

Methadone maintenance has become the treatment of choice for heroin addiction because of its beneficial effects on illicit opiate use and criminality. Yet methadone maintenance falls short in a variety of ways; methadone clients continue to use drugs, experience high rates of psychopathology and alcoholism, and fail to become employed and integrated into the community. These problems are endemic in addicts, but also can be attributed to a host of strategic and tactical failures in methadone maintenance treatment itself. Traditional counseling is an inadequate and confused way to provide clients with the living skills, psychotherapy, and limit setting they need. S.T.A.R. is a methadone program in Portland, Oregon, that emphasizes direct training of educational, recreational, and personal skills. Group treatment is employed to create social support for clients while psychotherapy and crisis counseling are available on an as-needed basis. Implementation of the model has caused some difficulties and has led to creative and promising results.

Activities of Daily Living↗
PubMed1988

Personality, drug use, and early attrition from substance abuse treatment.

This study examined the relationships among demographics, personality variables, drug use, and early attrition from substance abuse treatment. Attrition was considered at two time intervals; immediately (after one visit) and after 2 months. One hundred consecutive admissions to a community drug-abuse treatment center were given the MCMI and the SCL-90R following a standard intake interview. Subjects were classified according to their primary drug of abuse, yielding 16 opiate, 16 amphetamine, 34 cocaine, and 29 marijuana abusers. ANOVA's, ANCOVA's, and chi-squares were performed to compare characteristics of the different groups. Immediate Dropouts were less likely to be court mandated than Remainers, but were not different on any other demographic or drug use variable. Remainers had higher scores than Immediate Dropouts on 7 MCMI scales. A significant interaction between drug type, symptom severity, and early attrition was found for amphetamine abusers with high levels of subjective distress as measured by the SCL-90R. These clients dropped out earlier than amphetamine abusers without elevated SCL-90R scores. Analysis also indicated that Long-Term Remainers were less likely to be employed than Dropouts. All other comparisons between these groups failed to produce significant differences. This study confirms earlier research which found a high rate of early attrition from treatment with substance-abusing clients. Results also indicate that severity of psychopathology is not key in predicting attrition; it is more the nature of the disorder that influences client dropout. It is argued that continuation in community treatment is problematic for most substances abusers, and treatment facilities should routinely employ attrition prevention procedures.

Adult↗
PubMed1987

Multicopy expression vectors carrying the lac repressor gene for regulated high-level expression of genes in Escherichia coli.

A series of new expression vectors (the pTTQ series) has been constructed for the regulated expression of genes in Escherichia coli. Based on the pUC plasmids, the pTTQ vectors contain a polylinker/lacZ alpha region flanked by the strong hybrid trp-lac (tac) promoter and the rrnB transcription terminator. Foreign genes can be inserted into the polylinker region of this expression cassette, to give either transcriptional or translational fusions within the lacZ alpha coding region. In most commonly used strains of E. coli, multiple copies of the lac operator titrate out the lac repressor. This phenomenon leads to significant expression from tac or lac promoters present on multicopy plasmids, even in the absence of inducers such as IPTG. To ensure maximal repression of the tac promoter on the pTTQ vectors in any host strain, the lacIQ allele of the lac repressor gene was added to the vectors. This makes them particularly useful for cloning genes when expression at high level is desired but is detrimental to cell growth.

Escherichia coli↗
PubMed1986

The killer toxin of Kluyveromyces lactis: characterization of the toxin subunits and identification of the genes which encode them.

The killer character of the yeast Kluyveromyces lactis is associated with the presence of the linear DNA plasmids k1 and k2 and results from the secretion of a protein toxin into the growth medium. We find that toxin activity co-purifies with three polypeptides which we have termed the alpha- (mol. wt 99,000), beta- (mol. wt 30,000) and gamma- (mol. wt 27,500) subunits. The alpha-subunit appears to contain a single asparagine-linked oligosaccharide chain but neither of the smaller subunits is glycosylated. The N-terminal amino acid sequence of each subunit has been determined. Comparison of these data with the DNA sequence of plasmid k1 indicates that it encodes all three subunits. The alpha- and beta-subunits must be processed from the primary translation product of a single gene by an enzyme related to the KEX2 endopeptidase of Saccharomyces cerevisiae.

Amino Acid Sequence↗
PubMed1985

A mutation in an Escherichia coli ribosomal RNA operon that blocks the production of precursor 23 S ribosomal RNA by RNase III in vivo and in vitro.

We have isolated on a multicopy plasmid a mutant rrnB ribosomal RNA operon containing a 130 base-pair deletion immediately preceding the 23 S rRNA gene. The deletion shortens by just three base-pairs the 26 base-pair complementarity of the sequences that flank the 23 S rRNA gene, and which normally form an RNase III cleavage site in the rrnB primary transcript. Both in vivo and in vitro, cleavage at the altered RNase III site was almost completely abolished by the mutation. Our results therefore indicate that even a small perturbation of the double-stranded region normally recognized by RNase III strongly inhibits the action of the enzyme.

Autoradiography↗
PubMed1985

Mutations within the 23S rRNA coding sequence of E. coli which block ribosome assembly.

We have used site specific mutagenesis in vitro to construct a set of deletion mutations within the 5' region of a cloned 23S rRNA gene. In contrast to previously studied mutations in this gene, some of these deletions prevent the incorporation of 23S rRNA into ribosomal particles. This result is discussed in terms of a model in which interaction with the assembly initiator protein, L24, is perturbed.

Base Sequence↗
PubMed1985

General and specific psychotherapy role induction with substance-abusing clients.

The present study examined the effects of general and specific psychotherapy role induction on return rates and attendance in psychotherapy for substance-abusing clients. The subjects were 111 of 129 consecutive applicants to a community outpatient drug treatment center. Following a standard intake interview, clients received either a general psychotherapy role induction or a drug treatment specific role induction, or were placed in one of two control conditions. Results indicated that clients who received role induction procedures were more likely than controls to return after the intake interview. Furthermore, clients who received the drug treatment specific role induction returned at a significantly higher rate than all other clients. Analysis of attendance rates after 3 months showed that role induction had no effect on continuation in treatment.

Adolescent↗
PubMed1984

Interaction of ribosomal proteins S6, S8, S15 and S18 with the central domain of 16 S ribosomal RNA from Escherichia coli.

The co-operative interaction of 30 S ribosomal subunit proteins S6, S8, S15 and S18 with 16 S ribosomal RNA from Escherichia coli was studied by (1) determining how the binding of each protein is influenced by the others and (2) characterizing a series of protein-rRNA fragment complexes. Whereas S8 and S15 are known to associate independently with the 16 S rRNA, binding of S18 depended upon S8 and S15, and binding of S6 was found to require S8, S15 and S18. Ribonucleoprotein (RNP) fragments were derived from the S8-, S8/S15- and S6/S8/S15/S18-16 S rRNA complexes by partial RNase hydrolysis and isolated by electrophoresis through Mg2+-containing polyacrylamide gels or by centrifugation through sucrose gradients. Identification of the proteins associated with each RNP by gel electrophoresis in the presence of sodium dodecyl sulfate demonstrated the presence of S8, S8 + S15 and S6 + S8 + S15 + S18 in the corresponding fragment complexes. Analysis of the rRNA components of the RNP particles confirmed that S8 was bound to nucleotides 583 to 605 and 624 to 653, and that S8 and S15 were associated with nucleotides 583 to 605, 624 to 672 and 733 to 757. Proteins S6, S8, S15 and S18 were shown to protect nucleotides 563 to 605, 624 to 680, 702 to 770, 818 to 839 and 844 to 891, which span the entire central domain of the 16 S rRNA molecule (nucleotides 560 to 890). The binding site for each protein contains helical elements as well as single-stranded internal loops ranging in size from a single bulged nucleotide to 20 bases. Three terminal loops and one stem-loop structure within the central domain of the 16 S rRNA were not protected in the four-protein complex. Interestingly, bases within or very close to these unprotected regions have been shown to be accessible to chemical and enzymatic probes in 30 S subunits but not in 70 S ribosomes. Furthermore, nucleotides adjacent to one of the unprotected loops have been cross-linked to a region near the 3' end of 16 S rRNA. Our observations and those of others suggest that the bases in this domain that are not sequestered by interactions with S6, S8, S15 or S18 play a role involved in subunit association or in tertiary interactions between portions of the rRNA chain that are distant from one-another in the primary structure.(ABSTRACT TRUNCATED AT 400 WORDS)

Base Sequence↗
PubMed1984

Effects of site-directed mutations in the central domain of 16 S ribosomal RNA upon ribosomal protein binding, RNA processing and 30 S subunit assembly.

Using a multicopy plasmid encoding the Escherichia coli rrnB ribosomal RNA operon and the techniques of in vitro site-directed mutagenesis, we have introduced several small alterations into the central domain of 16 S rRNA, which encompasses nucleotides 560 to 890. Four of the rRNAs studied contained deletions and one contained an insertion. The altered small ribosomal subunit rRNAs were used to investigate relationships among 16 S rRNA processing, protein-16 S rRNA interactions and assembly of the 30 S ribosomal subunit. Analysis of plasmid-coded transcripts from maxicells revealed that products from wild-type 16 S rRNA genes were fully processed and assembled into mature 30 S subunits. Under the same conditions, the processing and assembly of transcripts derived from the mutant plasmids were severely impaired. In some instances, the mutations completely blocked both processes, while in other cases rRNA maturation and ribosome assembly were retarded, but not eliminated completely. In all cases, the mutations led to the accumulation of the 17 S precursor to 16 S rRNA. The mutant 17 S rRNAs were purified and incubated with various combinations of E. coli ribosomal proteins S6, S8, S15 and S18, which are known to bind to the central domain of 16 S rRNA. Ribonuclease digestion of the resulting protein-17 S rRNA complexes and fractionation of the products permitted detection of three distinct protein-RNA fragment complexes which contained S8, S8 + S15, or S6 + S8 + S15 + S18. Whereas wild-type 17 S rRNA was able to form all three of these complexes, deletion of nucleotides 693 to 721 or 822 to 874 abolished the interaction of S6 and S18, and removal of nucleotides 659 to 718 prevented the binding of S6, S15 and S18. In contrast, elimination of residue 614, or the presence of a 16-base insertion between nucleotides 614 and 615, had no significant effect on the binding of any of the four proteins tested. Together, our results demonstrate that 16 S rRNA maturation and 30 S subunit assembly are tightly coupled, and show that, in at least some cases, defects in these processes can be correlated with the inability of particular ribosomal proteins to associate with altered rRNA molecules. Moreover, we have confirmed the essentiality of certain rRNA sequences for the formation and/or stabilization of these protein-rRNA interactions.(ABSTRACT TRUNCATED AT 400 WORDS)

Centrifugation, Density Gradient↗
PubMed1984

Nucleotide sequence and transcription analysis of a linear DNA plasmid associated with the killer character of the yeast Kluyveromyces lactis.

In killer strains of the yeast Kluyveromyces lactis, production of a protein toxin which inhibits the growth of sensitive yeast cells is associated with the presence of two linear DNA plasmids, k1 and k2. We have determined the nucleotide sequence of the smaller plasmid k1 (8.9kb) which is thought to carry the structural gene(s) encoding the toxin. The plasmid has a low G + C content (26.8%) and contains four long open reading frames which account for over 95% of the total sequence. The longest open reading frame (1146 amino acids) probably corresponds to a structural gene for the killer toxin. Transcripts from three of the putative genes have been detected in K.lactis by Northern hybridisation.

Amino Acid Sequence↗
PubMed1983

Regions of DNA involved in the stringent control of plasmid-encoded rRNA in vivo.

We have examined the transcription of two plasmid-encoded, stable RNAs; a shortened 16S ribosomal RNA and the spacer transfer RNA2Glu from the Escherichia coli rrnB operon. Plasmid deletions were constructed in vitro, in order to examine the DNA regions required for stringent control of rRNA expression in vivo during amino acid starvation. We find that rRNA synthesized from plasmids does exhibit a relA-dependent, stringent response. The DNA sequences required for this regulation do not extend beyond 20 bases downstream of the P1 transcription initiation site. Deletion of P2, the second of the two tandem rRNA promoters, does not weaken the stringent control of transcripts from P1. These results demonstrate that pause sites for RNA polymerase identified in vitro do not play a significant role in the stringent control of rRNA synthesis in vivo and imply that stringent regulation takes place at the level of initiation, rather than elongation, of transcription. Surprisingly, we find that the presence of extra intact rrnB operons (carried by a multicopy plasmid) reduces the magnitude of the stringent response.

Amino Acids↗
PubMed1982

The mode of action of berninamycin and mechanism of resistance in the producing organism, Streptomyces bernensis.

The mode of action of berninamycin on bacterial protein synthesis is related to that of thiostrepton, a dissimilar compound. Both antibiotics bind to the complex of 23S RNA with protein L11 and both affect various functions of the ribosomal A site. Also, Streptomyces bernensis and Streptomyces azureus (which, respectively, produce berninamycin and thiostrepton) possess similar ribosomal RNA methylases capable of rendering ribosomes resistant to these compounds. Resistance involves specific pentose-methylation of 23S ribosomal RNA.

Anti-Bacterial Agents↗
PubMed1980

Coenzyme A is required for rat liver fatty acid synthetase activity.

Inhibition of highly purified rat liver fatty acid synthetase occurs when it is assayed in the presence of the ATP citrate lyase reaction components. Citrate, Mg2+, ATP, and ATP citrate lyase were all necessary for the inhibition to take place. Inhibition was prevented by hydroxycitrate, a competitive inhibitor for ATP citrate lyase. The length of time for the onset of inhibition to take place was proportional to the ratio of ATP citrate lyase activity to the fatty acid synthetase activity. The inhibition was reversed by the addition of coenzyme A. This indicates a reaction mechanism for fatty acid synthetase which involves free coenzyme A. Two possible roles for CoA are discussed, one as an allosteric activator and the other in the cleavage of palmitoyl enzyme in the last step of the reaction.

ATP Citrate (pro-S)-Lyase↗
PubMed1980

Functional homology between E. coli ribosomal protein L11 and B. megaterium protein BM-L11.

Ribosomes from the thiostrepton-resistant mutant MJ1 of Bacillus megaterium completely lack a protein designated BM-L11. When assayed in vitro, such ribosomes show an impaired ability to hydrolyse GTP in the presence of the elongation factor EF-G and are unable to support the synthesis of (p)ppGpp in response to the stringent factor. Restoration of both these activities can be achieved by re-addition of either protein BM-L11 or its serological homologue from Escherichia coli, protein L11, implying that these two proteins are related functionally as well as immunologically.

Bacillus megaterium↗