Biomedical subjects

M R Schaefer

Publications and source records attributed to M R Schaefer.

23 records · Page 2Linked to original sources

PubMed1990

Different and rapid responses of four cyanobacterial psbA transcripts to changes in light intensity.

The genome of the cyanobacterium Synechococcus sp. strain PCC 7942 contains three psbA genes which encode two forms of the D1 protein of photosystem II. Experiments using psbA-lacZ translational fusions and Western blot (immunoblot) analysis have shown that the psbA genes respond differently to changes in light intensity, altering the ratio of the two forms of D1 in the thylakoid membrane. Each gene produces a 1.2-kilobase (kb) mRNA. A probe specific for psbAII transcripts also identified a 1.6-kb mRNA which starts 419 base pairs upstream of the 5' end of the 1.2-kb species and overlaps the entire 1.2-kb transcript. This 419-base-pair region includes an open reading frame (ORF1) of 114 amino acids. We investigated the effects of changes in light intensity on psbAII transcript levels in a series of light shift experiments in the wild-type Synechococcus sp. and in AMC084, a mutant which does not produce the 1.6-kb transcript. After exposure to high light intensities for 15 min, the level of the 1.2-kb psbAII transcript increased in both strains. This transcript was not detected in either strain after transfer to low light intensity. The psbAIII transcript showed the same pattern of response as the 1.2-kb psbAII transcript, whereas the 1.6-kb psbAII transcript was unaffected by different light intensities. The psbAI transcript levels responded oppositely to those of psbAII and psbAIII. These data, considered along with previous results obtained by using lacZ translational gene fusions, indicate that the response of psbA genes to changes in light intensity is controlled primarily at the transcriptional level.

Amino Acid Sequence↗

PubMed1989

Light availability influences the ratio of two forms of D1 in cyanobacterial thylakoids.

The psbA multigene family in Synechococcus sp. strain PCC 7942 encodes two forms of the D1 protein; Form I, the product of psbAI, differs from Form II, the product of psbAII and psbAIII, at 25 of 360 amino acid positions. D1 is essential for photosynthesis as a protein component of the photosystem II reaction center. Antisera were raised against purified hybrid proteins encoded by psbAI-lacZ and psbAIII-lacZ translational gene fusions that contain the unique amino termini of Form I and Form II, respectively. Form specificity of each antiserum was verified by Western analysis using thylakoid membranes from mutant strains containing only Form I or Form II. Western analysis of thylakoid membranes from wild-type cells cultured at different light intensities detected both forms of D1 in the membrane and showed changes in the ratio of the two forms. The D1 composition of the membrane matched predicted ratios of the forms based on differential gene expression: psbAI is expressed highest at low light, and both psbAII and psbAIII are expressed highest at high light. Along a gradient of light intensity from 5 microE. m-2.s-1 to 482 microE.m-2.s-1, the relative amount of Form I in thylakoid membranes decreased 58%, while the relative amount of Form II increased 60%. Maximum detection of Form I coupled with minimum detection of Form II in membranes from cells harvested at light intensities below 390 microE.m-2.s-1 suggests a central role for Form I in photosystem II. Increased incorporation of Form II into the thylakoid membrane occurred at light intensities reported by others to be photoinhibitory, suggesting that Form II serves a role in adaptation to high light.

Chlorophyll↗

PubMed1989

Differential expression of members of a cyanobacterial psbA gene family in response to light.

The genome of the cyanobacterium Synechococcus sp. strain PCC 7942 contains three psbA genes encoding two forms of the D1 protein: form I, the product of psbAI, differs from form II, the product of both psbAII and psbAIII, at 25 of 360 residues. D1 is essential for photosynthesis as a core component of the photosystem II reaction center. Translational gene fusions between each of the Synechococcus psbA genes and the Escherichia coli lacZ gene were inserted into the chromosome of wild-type Synechococcus sp. at the respective psbA loci to serve as in vivo reporters of psbA expression. beta-Galactosidase activities indicated differential expression of the psbA-lacZ gene fusions related to light availability. Expression of psbAI was 500-fold greater than expression of psbAII and 50-fold greater than psbAIII under similar conditions. As light intensity decreased from 600 microE.m-2.s-1 to 2 microE.m-2.s-1, expression of the psbAI reporter increased eightfold while expression of the psbAII and psbAIII reporters decreased 10-fold, suggesting differential production of the two forms of D1 in photosystem II in response to light availability. Relative levels of psbA-lacZ fusion transcripts directly reflected beta-galactosidase activities in the transformants, although the fusion transcripts were less stable than native psbA messages.

Chlorophyll↗

PubMed1988

Prevalence of childhood physical abuse in adult male veteran alcoholics.

Although past research has identified psychological and behavioral consequences for adults who were abused as children, few studies have examined the incidence and consequences of childhood physical abuse among adult alcoholics. The purpose of this study was to assess the prevalence of a childhood history of physical abuse in adult male alcoholics and to determine what differences may exist in the psychological profile and patterns of alcohol abuse in abused and nonabused alcoholics. The study sample was comprised of 100 male alcoholic inpatients from the alcoholism treatment unit at a metropolitan Veterans Administration hospital. Subjects were administered a self-report devised by the authors to assess a history of childhood physical abuse, the Michigan Alcoholism Screening Test (MAST), the Severity of Alcohol Dependence Questionnaire (SADQ), and the Symptom Checklist-90-Revised (SCL-90-R). Findings indicated that approximately one-third of the alcoholics were physically abused as children. Abused alcoholics reported having more severe psychological symptoms and distress than their nonabused counterparts, although they did not differ on the onset, severity, or treatment history for alcohol dependency.

Adult↗

PubMed1987

Severity of alcohol dependence and its relationship to additional psychiatric symptoms in male alcoholic inpatients.

Many alcoholics suffer from distress associated with psychiatric symptoms in addition to alcoholism. Although there may be many such symptoms reported by the alcoholic, there may not be enough in any one category to meet DSM III criteria for an additional psychiatric diagnosis, and consequently these symptoms may not be considered in treatment planning. In addition, the prevalence and severity of psychiatric symptoms may be dependent on the progression of alcoholism. The purpose of this study was to examine whether a relationship exists between patterns of psychiatric symptomatology and the level of severity of alcohol dependence in an inpatient male alcoholic sample, and to describe how this information can be utilized to differentiate large groups of alcoholics into clinical meaningful categories. The study sample was comprised of 100 male alcoholic inpatients from the Alcoholism Treatment Unit at a metropolitan Veterans Administration Hospital. Subjects were administered The Michigan Alcoholism Screening Test (MAST), the Severity of Alcohol Dependence Questionnaire (SADQ), and the Symptom Checklist-90-Revised (SCL-90-R). Correlational analysis of the data supported the hypothesis that a positive relationship exists between the severity of alcohol dependence and the prevalence of additional psychiatric symptom patterns. Partial correlational analysis indicated that the length of the alcoholic's illness and the number of inpatient treatments for alcoholism enhanced the relationship between the severity of alcoholism and most of the symptom scales. The utility of assessing concurrent psychiatric symptomatology as it relates to the severity of alcohol dependence is discussed in relation to treatment planning and prognostic assessment of the patient.

Adult↗