Hitching a ride.
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Chromosomal Proteins, Non-Histone↗
Biomedical subjects
Elaine Yeh
Publications and source records attributed to Elaine Yeh.
Clinical, epidemiologic, and environmental surveillance for ehrlichiosis and anaplasmosis in an endemic area of northern California.
Two forms of tick-borne leukocytotropic rickettsioses have been recognized in California since the mid-1990s: human monocytic ehrlichiosis (HME) caused by Ehrlichia chaffeensis and human granulocytic anaplasmosis (HGA) caused by Anaplasma phagocytophilum. Between 1997 and 1999, two cases of HME and four cases of HGA were diagnosed in residents of southern Humboldt County, California. Environmental followup at case-patients' residences revealed dense populations of Ixodes pacificus ticks, particularly in grassy roadside areas. PCR evidence of A. phagocytophilum was detected in approximately 2.0% of I. pacificus; E. chaffeensis was not detected in any of 625 ticks tested. Serologic antibody to A. phagocytophilum was detected in two of 54 participants in a community epidemiologic study; one of these also had antibody to E. chaffeensis. Over 85% of study participants reported finding a tick on themselves in the preceding 12 mo. Residents of southern Humboldt County are at significant risk of tick bites and should take appropriate prevention measures to avoid infection with rickettsia and other tick-transmitted pathogens.
Adolescent↗
Stable kinetochore-microtubule attachment constrains centromere positioning in metaphase.
With a single microtubule attachment, budding-yeast kinetochores provide an excellent system for understanding the coordinated linkage to dynamic microtubule plus ends for chromosome oscillation and positioning. Fluorescent tagging of kinetochore proteins indicates that, on average, all centromeres are clustered, distinctly separated from their sisters, and positioned equidistant from their respective spindle poles during metaphase. However, individual fluorescent chromosome markers near the centromere transiently reassociate with their sisters and oscillate from one spindle half to the other. To reconcile the apparent disparity between the average centromere position and individual centromere proximal markers, we utilized fluorescence recovery after photobleaching to measure stability of the histone-H3 variant Cse4p/CENP-A. Newly synthesized Cse4p replaces old protein during DNA replication. Once assembled, Cse4-GFP is a physically stable component of centromeres during mitosis. This allowed us to follow centromere dynamics within each spindle half. Kinetochores remain stably attached to dynamic microtubules and exhibit a low incidence of switching orientation or position between the spindle halves. Switching of sister chromatid attachment may be contemporaneous with Cse4p exchange and early kinetochore assembly during S phase; this would promote mixing of chromosome attachment to each spindle pole. Once biorientation is attained, centromeres rarely make excursions beyond their proximal half spindle.
Centromere↗
Nuclear oscillations and nuclear filament formation accompany single-strand annealing repair of a dicentric chromosome in Saccharomyces cerevisiae.
Dicentric chromosomes undergo breakage during mitosis as a result of the attachment of two centromeres on one sister chromatid to opposite spindle poles. Studies utilizing a conditional dicentric chromosome III in Saccharomyces cerevisiae have shown that dicentric chromosome repair occurs primarily by deletion of one centromere via a RAD52-dependent recombination pathway. We report that dicentric chromosome resolution requires RAD1, a gene involved in the single-strand annealing DNA repair pathway. We additionally show that single-strand annealing repair of a dicentric chromosome can occur in the absence of RAD52. RAD52-independent repair requires the adaptation-defective cdc5-ad allele of the yeast polo kinase and the DNA damage checkpoint gene RAD9. Dicentric chromosome breakage in cdc5-ad rad52 mutant cells is associated with a prolonged mitotic arrest, during which nuclei undergo microtubule-dependent oscillations, accompanied by dynamic changes in nuclear morphology. We further demonstrate that the frequency of spontaneous direct repeat recombination is suppressed in yeast cells treated with benomyl, a drug that perturbs microtubules. Our findings indicate that microtubule-dependent processes facilitate recombination.
Benomyl↗
A high-resolution multimode digital microscope system.
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Animals↗