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J C Thomas

Publications and source records attributed to J C Thomas.

At least 19 recordsLinked to original sources
PubMed1992

Characterization of the genes encoding phycoerythrin in the red alga Rhodella violacea: evidence for a splitting of the rpeB gene by an intron.

The phycobilisome of the eukaryotic unicellular red alga Rhodella violacea presents in some respects an organization that is intermediate between those of the homologous counterparts found in cyanobacteria (the putative chloroplast progenitor) and more advanced, pluricellular red algae. This suggests evolutionary relationships that we investigated at the genome level. The present work describes the sequences of two rhodophytan phycobilisome genes, rpeA and rpeB. These chloroplast genes encode the alpha and beta subunits of phycoerythrin, the major component of the light-harvesting antennae and one of the most abundant cellular proteins in these algae. The amino acid sequences deduced from both rpeA and rpeB present strong homologies with those previously reported for phycoerythrin subunits of cyanobacteria, rhodophyta, and cryptomonads. The main difference with the corresponding cyanobacterial genes was the unexpected occurrence of an intervening sequence that split rpeB into two exons. This intervening sequence presents characteristics of group II introns but lacks several structural domains. Transcriptional analyses showed that the two rpe genes are cotranscribed and that the major RNA species detected corresponds to a mature mRNA lacking the intron. As the phycobiliproteins form a group of closely related polypeptides in cyanobacteria and rhodophyta, the molecular events affecting the corresponding genes, such as the rpeB intron, may be a clue to elucidate some aspects of the molecular processes involved in the evolution of plastid genes.

Amino Acid Sequence↗
PubMed1992

Choosing an appropriate measure of diarrhoea occurrence: examples from a community-based study in rural Kenya.

Epidemiological studies which aim to identify protective or risk factors for diarrhoea may rely on any of several established measures of disease occurrence, including cumulative incidence, (CI), incidence density (ID), and point prevalence (P); each with its own strengths and limitations. Comparison of these measures was afforded by a community-based study in rural Kenya in which the incidence and prevalence of diarrhoea were measured simultaneously but by independent means in the same group of children. In a cohort study, CI and ID among 138 infants (aged 0-6 months) were 26.1% and 1.41 episodes per 100 infant-weeks, respectively. Among 111 toddlers (aged 18-29 months) CI and ID were 39.6% and 1.96 episodes per 100 toddler-weeks, respectively. In a cross-sectional study of these children, the Ps among infants and toddlers were 9.8 and 6.1%, respectively. Data on incident cases required more time and resources to obtain and evidenced more underreporting of diarrhoea episodes relative to the prevalence data. Other community-based studies have reported the ID of diarrhoea five times more often than any other measure, but appear to have calculated ID incorrectly. The infrequency with which CI and P are reported does not reflect their actual utility.

Child, Preschool↗
PubMed1992

Human immunodeficiency virus-1 seroprevalence among parturients in Los Angeles County public hospitals.

To estimate the prevalence of human immunodeficiency virus type 1 (HIV-1) among parturients in an area with a high cumulative incidence of AIDS, an HIV seroprevalence study was conducted in 1988 in Los Angeles County. Test results were available from 8485 (86.1%) of the 9860 women delivering at four public hospitals. The test results were linked to demographic and medical information available from routinely collected delivery records. Three specimens were HIV-positive, for a seroprevalence of 3.5 per 10,000. The seropositive women were all Latina. The prevalence of HIV among women delivering at all hospitals in Los Angeles County has been shown to be relatively low compared with that of other metropolitan areas with a high number of AIDS cases, such as New York city, but appears to be even lower among women delivering at public hospitals during this time period. This low prevalence is attributed to the predominance of Latinas, who may have lower levels of infection, among public hospital parturients. The relatively low prevalence of HIV among injection drug users in Los Angeles County may contribute to the overall lower prevalence among women in Los Angeles County compared with those in New York city. This study supplements county-specific data obtained from statewide blinded neonatal testing by providing details on HIV seroprevalence among the catchment populations of public hospitals in Los Angeles County.

Acquired Immunodeficiency Syndrome↗
PubMed1991

Light-harvesting complexes of brown algae. Biochemical characterization and immunological relationships.

The pigment composition of the light-harvesting complexes isolated from several brown algae belonging to different orders has been analysed by reverse-phase HPLC. Relative to whole chloroplasts, they were markedly enriched in Chl c, fucoxanthin and violaxanthin and conversely depleted in Chl a. The relative molar proportions of the 4 main pigments (Chl a/Chl c/fucoxanthin/violaxanthin) ranged from 100:18:76:6 to 100:30:107:17. The protein moiety of LH complexes of all the species studied were composed of one or two main polypeptide components in the range of 19-22 kDa. These polypeptide subunits were arranged in polymeric particles about 240 kDa in Laminaria saccharina. A polyclonal antibody raised against the LH polypeptide of Fucus serratus has been tested on LH apoproteins of other Chromophytes and Chlorophytes. Phylogenic implications of these results are discussed.

Amino Acids↗
PubMed1991

Risk factors for carriage of meningococcus in the Los Angeles County men's jail system.

Ten cases of meningococcal meningitis in the Los Angeles County men's jail system in 1986 were the first known reported cases in this population. New cases have continued into 1990. Nineteen of 21 symptomatic cases identified by serogroup from the men's jail occurring through 1988 had serogroup C. The prevalence of meningococcal carriage and potential risk factors were studied in 1988 among 150 men booked to enter the jail, 350 inmates being released, and 100 jail staff. The prevalence of meningococcal carriage among releases, bookings, and staff were 25.4%, 18.7%, and 5.0%, respectively. Among releases, imprisonment longer than a threshold of 28 days increased carriage of serogroup C 10.0 times (95% confidence interval (CI) 4.6-21.6). Among bookings, household crowding increased serogroup C carriage 8.2 times (95% CI 1.5-45.3). Direct and passive smoking at home increased carriage of any serogroup 5.2 (95% CI 1.2-47.5) and 2.5 (95% CI 1.1-5.8) times, respectively. Feasible potential interventions include banning smoking in the jail and immunization with quadrivalent meningococcal vaccine of booked men sentenced for one month or more.

Carrier State↗
PubMed1991

Ridge contour related to esthetics and function.

Maxillary anterior fixed prostheses may be compromised when pontics are adapted to deficient residual alveolar ridges. This study determined the effect of ridge contour on esthetics and function. Thirteen men and 17 women, 23 to 75 years of age, who had received maxillary anterior fixed prostheses during the period 1976 to 1986 participated. A six-item structured interview was conducted for each subject to determine causes of satisfaction or dissatisfaction with esthetics and function. Pontic esthetics were also determined by examination using a 12-point esthetic index that was developed and pretested for this study. Residual ridge contour was classified according to Siebert as being deficient buccolingually (I), deficient apicocoronally (II), or deficient in both areas in combination (III). The results showed that patients with class I ridges had a higher subjective level of satisfaction with their prosthesis than did those with class II or III ridges. Esthetic index scores were significantly higher (p less than 0.05) for type I (10) than for type II (7.4) or III (7.3) using a post hoc Scheffé comparison. These results suggest that consideration be given to ridge augmentation prior to construction of maxillary anterior fixed prostheses, particularly when class II or III defects are present.

Adult↗
PubMed1991

Measles vaccination coverage among Latino children aged 12 to 59 months in Los Angeles County: a household survey.

A high rate of measles transmission has occurred in Los Angeles County since 1987. To determine measles vaccination coverage among Latino preschoolers, the group at highest risk of measles during this period, a cluster survey was conducted among Latino households with children aged 12 to 59 months. Of 279 children enrolled, 240 (86%, 95% confidence interval = 81% to 91%) reportedly had received the measles vaccine. Measles vaccination coverage among Latino preschoolers in Los Angeles County is insufficient to halt measles transmission within this subpopulation.

Child, Preschool↗
PubMed1991

H-2 (I-A) control of the antibody repertoire to secreted antigens of Trichinella spiralis in infection and its relevance to resistance and susceptibility.

Humans infected with the parasitic nematode Trichinella spiralis vary in the specificity of their antibody responses to the antigens of the parasite. The possibility that such host variation in antigen recognition has a genetic basis was examined in infected inbred mice whose antigen recognition profiles were characterized by immunoprecipitation of biosynthetically labelled secreted materials of adult parasites and SDS-PAGE. The strains varied considerably in repertoire and none produced detectable antibody to all the potential antigens. Using a panel of H-2 congenic and recombinant strains it was established that the repertoire was determined by the major histocompatibility complex (MHC), the I-A region in particular. Other factors, such as level of infection and variation between individuals, affected antigen recognition profiles, but this was always within limits imposed by the MHC. Lastly, an attempt to correlate antibody repertoire with relative susceptibility or resistance to T. spiralis failed to reveal any clear association. This also applied to the AKR/J and AKR-Fv-1b strains, which are H-2-identical but differ in a non-MHC susceptibility locus. These findings would argue, therefore, that the I-A region controls the antibody repertoire in this nematode infection but that the repertoire overall has little influence on the efficiency with which the infections are controlled by the immune system. Should this also apply for other nematode infections, then antigen recognition profiles of infected individual humans and domestic animals might not, therefore, be useful indicators of relative resistance or susceptibility to infection.

Animals↗
PubMed1990

Evidence for allosteric transitions in secondary structure induced by superhelical stress.

Previous studies suggest that the global secondary structures of native supercoiled and equilibrium linear DNAs may differ somewhat. Recent evidence also indicates that metastable secondary structure commonly persists following complete relaxation of the superhelical stress by intercalating dyes or by the action of topoisomerase I. In this work, the torsion constants (alpha) of pBR322, pUC8 and M13mp7 (replicative form) DNAs are determined by time-resolved fluorescence polarization anisotropy at various times subsequent to linearization. In all three cases, the torsion constants are relatively low immediately after linearization, and evolve for eight to ten weeks before reaching their apparent equilibrium values. It is shown in detail how the persistence of metastable secondary structure, subsequent to relaxation of superhelical stress, necessarily implies that one or more transitions in equilibrium secondary structure are induced as the superhelix density is varied from zero to native, or vice versa. Samples of pUC8 dimer (5434 base-pairs) with different superhelix densities are prepared by the action of topoisomerase I in the presence of various amounts of ethidium. Their median linking number differences are determined by standard band counting methods. The translational diffusion coefficient (Do) and the plateau diffusion coefficient (Dplat) characterizing internal motions over short distances (225 A) are determined by dynamic light-scattering. The torsion constant (alpha) between base-pairs and the circular dichroism spectrum are also measured for each sample. Curves of Dplat, Do, alpha and molar ellipticity ([theta]) (at the minimum near 250 nm) versus superhelix density (sigma) are constructed. The curve of Do versus sigma is very similar to that for sedimentation coefficient versus sigma for simian virus 40 (SV40) and polyoma DNAs. The curves of Dplat, Do, alpha and [theta] versus sigma show that, with increasing negative superhelix density, a structural transition occurs near sigma = -0.020 to an intermediate state with low torsion constant, and a second structural transition occurs near sigma = -0.035 to a state that exhibits more normal properties by sigma = -0.048. These data are consistent with the hypothesis that supercoiling induces two successive allosteric transitions to alternative global secondary structures. The data are much less consistent with the hypothesis that supercoiling induces some radical secondary structure at one or a few sites of small extent at sigma = -0.020, and at other sites at sigma = -0.035, or with hypotheses based on changes in tertiary structure alone.(ABSTRACT TRUNCATED AT 400 WORDS)

Circular Dichroism↗
PubMed1989

Expression of DNA binding proteins in carrot somatic embryos that specifically interact with a cis regulatory element of the French bean phaseolin gene.

Nuclear proteins from bean (Phaseolus vulgarus) embryos bind specifically to a 55 bp DNA sequence located upstream of the seed storage protein gene phaseolin. This sequence is capable of elevating gene expression in transgenic tobacco plants by as much as 150-fold when fused to a chimeric beta-glucuronidase reporter gene. Results presented in this paper demonstrate that nuclear extracts from carrot embryos bind to a phaseolin DNA sequence that includes a phaseolin activator sequence. This specific DNA binding activity is modulated during somatic embryogenesis. Two separable protein species react specifically with the labeled phaseolin DNA fragment (58.0 and 51.7 kDa). These results suggest that the cis- and trans-acting elements controlling gene expression have been highly conserved during evolution.

DNA↗
PubMed1989

Transmission and control of methicillin-resistant Staphylococcus aureus in a skilled nursing facility.

Methicillin-resistant Staphylococcus aureus (MRSA) is increasingly frequent in both acute care facilities (ACFs) and skilled nursing facilities (SNFs). Admissions to SNFs from ACFs with endemic MRSA are one likely source of infection in SNFs. The occurrence of MRSA in SNFs and the relative roles of ACFs and SNFs in MRSA transmission have not been well characterized. We conducted an epidemiologic investigation in an SNF reporting a high incidence of MRSA cases and found that the prevalence of MRSA exceeded that reported in acute care settings. Fifteen (9.1%) of the 164 residents were colonized or infected with MRSA. Risk factors for MRSA identified through a prevalence case-control study were nasogastric intubation (odds ratio = 5.5; 95% confidence interval = 1.2, 26.4), antibiotic therapy (OR = 3.9; CI = 1.2, 13.0), and hospitalization in an acute care facility within the previous six months (OR = 2.9; CI = 0.9, 9.7). During a three-month period, 6 of 100 new admissions were MRSA-positive; all positive patients were from ACFs. Five new cases also emerged from previously MRSA-negative residents. SNF residents are often discharged to ACFs. Transmission of MRSA within the SNF and the transfer of patients to ACFs increases the reservoir of potentially infective patients and the potential for MRSA infections in ACFs. Modest control measures, including targeted surveillance culturing and cohorting of colonized residents, may minimize MRSA transmission in the SNF and decrease the reservoir of MRSA in the community.

Aged↗
PubMed1989

The Wiltse pedicle screw fixation system. Early clinical results.

Ninety-nine patients were studied prospectively after spine fusion augmented with the Wiltse pedicle screw fixation system. Follow-up ranged from 12 to 34 months, averaging 20 months. There were 33 men and 66 women. Their ages ranged from 20 to 86, with the average age of 52. This was the first spine surgery in 23 patients. Seventy-six patients had had prior spine surgery. Spine fusion was attempted at one to four levels of the lumbosacral spine. Major perioperative complications were seen in seven patients (7%). Hardware failure was seen in seven cases (7%). Union was assessed by radiographs at 1 year or more after surgery in 82 patients (85%). In those 82 patients, union was seen in 56 (68%) and nonunion in 26 (32%). Change in lordosis was measured in 54 patients. The average change was a loss of 1.7 degrees lordosis per level fused. A questionnaire was answered by 79 patients (81%). Overall, 55 (70%) stated that they had some benefit from surgery, ten (13%) had no change, and 13 (17%) were worse.

Adult↗
PubMed1989

In situ arthrodesis without decompression for Grade-III or IV isthmic spondylolisthesis in adults who have severe sciatica.

Eight adults who had back pain and sciatica that was caused by Grade-III or IV isthmic spondylolisthesis of the fifth lumbar vertebra on the sacrum were treated consecutively by in situ arthrodesis without decompression. The anterior displacement of the fifth lumbar vertebra averaged 82 per cent (range, 66 to 118 per cent). The length of follow-up averaged 5.5 years (range, two to fourteen years). All of the arthrodeses resulted in a solid fusion and excellent relief of both the back pain and the sciatica. All of the preoperative neurological deficits resolved, with the exception of a decreased or absent Achilles-tendon reflex in two patients. There were no complications, and all of the patients returned to their preoperative occupations.

Adult↗