Similarities in Restriction Fragment Patterns of Mitochondrial DNAs of PhytophthoraSpecies Strongly Depend on the Restriction Enzyme Used Due to Heterogeneous Base Distribution and Sequence Conservation

Mitochondrial DNAs of six morphologically different Phytophthora species were digested with 15 restriction enzymes. The numbers of restriction fragments obtained differed considerably from those theoretically expected for random base distribution. Enzymes with relatively many G and C in their recognition sequences produced significantly larger numbers of fragments. Moreover, fragments generated by most of these enzymes were more often shared by two or more species than those from enzymes with more A and T in their recognition sequence. It is concluded that base distribution in mitochondrial DNA of Phytophthora is heterogeneous,AT-rich stretches occurring scattered over the mitochondrial genome and GC-rich regions present in conserved sequences, presumably genes. A practical consequence for taxonomic RFLP studies is that optimal enzymes can be selected, depending on the desired level of resolution.     

Tetrapod phylogeny inferred from 18S and 28S ribosomal RNA sequences and a review of the evidence for amniote relationships [published erratum appears in Mol Biol Evol 1991 May;8(3):398]

The 18S ribosomal RNAs of 21 tetrapods were sequenced and aligned with five published tetrapod sequences. When the coelacanth was used as an outgroup, Lissamphibia (living amphibians) and Amniota (amniotes) were found to be statistically significant monophyletic groups. Although little resolution was obtained among the lissamphibian taxa, the amniote sequences support a sister-group relationship between birds and mammals. Portions of the 28S ribosomal RNA (rRNA) molecule in 11 tetrapods also were sequenced, although the phylogenetic results were inconclusive. In contrast to previous studies, deletion or down- weighting of base-paired sites were found to have little effect on phylogenetic relationships. Molecular evidence for amniote relationships is reviewed, showing that three genes (beta-hemoglobin, myoglobin, and 18S rRNA) unambiguously support a bird-mammal relationship, compared with one gene (histone H2B) that favors a bird- crocodilian clade. Separate analyses of four other genes (alpha- crystallin A, alpha-hemoglobin, insulin, and 28S rRNA) and a combined analysis of all sequence data are inconclusive, in that different groups are defined in different analyses and none are strongly supported. It is suggested that until sequences become available from a broader array of taxa, the molecular evidence is best evaluated at the level of individual genes, with emphasis placed on those studies with the greatest number of taxa and sites. When this is done, a bird-mammal relationship is most strongly supported. When regarded in combination with the morphological evidence for this association, it must be considered at least as plausible as a bird-crocodilian relationship.      

Recent Change in the Annual Pattern of Sexually Transmitted Diseases in the United States

This study analyzed the 1999 to 2003 database of the Center for Disease Control and Prevention (CDC) for seasonal and longer‐term time trends in the sexually transmitted diseases (STDs) of chlamydia, gonorrhea, and syphilis in the United States. Linear regression was used to ascertain time trends, and a linear mixed auto‐regression model was applied to determine the statistical significance of the major peaks relative to the annualized time series mean. A statistically significant increasing trend during the 5 yr span was documented only in the incidence of chlamydia. No clear annual periodicity was detected in any of the STDs; instead, significant three‐month cycles were documented in all the STDs, with prominent peaks evident in March, May, August, and November. The March and May peaks could be associated with the sexual activities of young adults during spring break, which for different colleges and universities, commences as early as mid‐ to late‐February and concludes as late as early‐ to mid‐April, when huge numbers of sexually active youth congregate at beach resort settings. We propose the August peak is representative of summer sexual activity, in particular, of youths during school recess when adult supervision is poor. Finally, the autumn peak seems to be an expression of an endogenous annual rhythm in human reproductive biology, exemplified by elevated levels of testosterone in young males and sexual activity at this time of the year.     

Adsorption of Al3+ to phosphatidylcholine vesicles

Aluminum toxicity to soil and aquatic organisms is widespread, but the mechanisms of toxicity are unknown. To understand these mechanisms, it is important to know how aluminum reacts with cell surfaces. In this report, we studied adsorption of Al3+ to liposomes composed of phosphatidylcholine, the most abundant phospholipid in plasma membranes of eukaryotic cells. Our equilibrium dialysis and electrophoresis experiments both showed that Al3+ has a 560-fold higher affinity for the phosphatidylcholine surface than Ca2+. Unlike previous reports for adsorption of divalent metals, adsorption of Al3+ to phosphatidylcholine was predicted only approximately by the Stern model. Adsorption of AlF2+ and AlF2+ to the surface was not detectable at the activities we used. From our data, we calculate that Al3+ at 5 x 10(-6) activity could neutralize the surface charge on plant cell plasma membranes and cause a surface potential shift from -30 to +11 mV. This is consistent with non-specific Al3+ inhibition of cation uptake by root cells. Al3+ adsorption to phosphatidylcholine may also play a role in aluminum uptake into cytoplasm by endocytosis.     

Seasonality of Primarily Childhood and Young Adult Infectious Diseases in the United States

The Center for Disease Control (CDC) in the United States collects and maintains records of communicable (so‐called notifiable) infectious diseases that cause significant morbidity and mortality and impact the national economy. This investigation focused on seasonal patterns in the primarily childhood and young adult infectious diseases of meningococcal meningitis, mumps, pertussis, typhoid fever, streptococcal toxic shock syndrome (1990 to 2003 CDC database), and varicella (1993 to 2003 CDC database). Linear regression was performed to ascertain the trend in the incidence of each disease, and multi‐component cosinor analysis was applied to determine and describe periodicities. Significant decreasing trends in incidence were detected in meningococcal meningitis, mumps, typhoid fever, and streptococcal toxic shock syndrome, and increasing trends were found in pertussis and varicella. Significant annual patterns were documented in meningococcal meningitis (January peak), mumps (April peak), pertussis (August peak), varicella (April peak), typhoid fever (August peak), and in the hospital‐acquired streptococcal toxic shock syndrome (February peak). Such seasonal patterns and long‐term trends in infectious diseases are of practical public health significance in indicating which can benefit from timely prevention interventions.     

Annual pattern of human conception in the State of Texas

A total of 2,828,068 State of Texas singleton conceptions, estimated from the date of the first day of the last menstrual period, were assessed for annual periodicity by multiple-component (1-yr fundamental plus the 6- and 3-month harmonics) Cosinor analysis. An annual pattern (p < 0.001) of conception was detected with a December peak, end of July-beginning of August trough and modest amplitude (total peak-to-trough variation) equal to 13.3% of the yearly mean. Annual patterns (p < 0.005) of generally comparable peak and trough times were also documented for conceptions categorized by maternal marital status, age, ethnicity, years of education, birthplace, and county (Texas-Mexico border vs. non-border) of residence. The amplitude, a measure of the prominence of the annual pattern, varied by race (two-fold greater for non-Hispanic Blacks and Hispanics than non-Hispanic Whites), age (50-60% greater for the 19-year-old and younger group than the 20-29 and 30-44-year-old groups) and maternal education (two-fold greater for those with 0-8 than 13 or more years of schooling). Annual patterns (p < 0.001) in conceptions, generally with December peak and end of July-beginning of August trough, were also detected for neonatal variables categorized by birth weight, birth order, gestational age, and gender. The amplitude of the annual pattern in conceptions varied directly with gestational age and inversely with birth weight class.     

Day-night pattern in accidental exposures to blood-borne pathogens among medical students and residents

The purpose of this study was to determine whether the occurrence of accidental blood-borne pathogen exposure incidents in medical students and residents in training varies during the 24 h. A retrospective review of reported exposures was conducted in a large urban teaching institution--the University of Texas Health Science Center in Houston--between November 1993 and July 1998. Professional level (year of student or level of resident), time of exposure, means/route of exposure (needle stick, laceration, or splash), and type of medical service were recorded. Analysis of the clock time of the 745 reported blood-borne pathogen exposures showed they occurred more frequently during the day than night. Over the nearly 5-year span, 531 incidents took place between 06:00 and 17:59 in comparison to only 214 between 18:00 and 05:59. To account for the day-night difference in medical student and resident hospital staffing, the data were reexpressed as exposure rates, that is, in terms of the number of events per hour per 1000 medical students and residents. Based on the total number of reported exposures over the almost 5-year span of data collection, the average rate was 40 accidents per hour per 1000 doctors in training during the 12 h daytime span (6:00-17:59). It was 50% greater at night (18:00-05:59), with 60 incidents per hour per 1000 doctors in training. The day-night difference in rate of exposures was statistically significant (p < .04). The relative risk ratio for residents and students when working during the day shift compared to working the night shift was 0.67. This means that doctors in training are at a 1.50 higher risk of sustaining a blood-borne pathogen exposure when working nights than when working days.