DNA damage triggers increased mobility of chromosomes in G1-phase cells

During S phase in Saccharomyces cerevisiae, chromosomal loci become mobile in response to DNA double-strand breaks both at the break site (local mobility) and throughout the nucleus (global mobility). Increased nuclear exploration is regulated by the recombination machinery and the DNA damage checkpoint and is likely an important aspect of homology search. While mobility in response to DNA damage has been studied extensively in S phase, the response in interphase has not, and the question of whether homologous recombination proceeds to completion in G1 phase remains controversial. Here, we find that global mobility is triggered in G1 phase. As in S phase, global mobility in G1 phase is controlled by the DNA damage checkpoint and the Rad51 recombinase. Interestingly, despite the restriction of Rad52 mediator foci to S phase, Rad51 foci form at high levels in G1 phase. Together, these observations indicate that the recombination and checkpoint machineries promote global mobility in G1 phase, supporting the notion that recombination can occur in interphase diploids.

Rad5 dysregulation drives hyperactive recombination at replication forks resulting in cisplatin sensitivity and genome instability

The postreplication repair gene, HLTF, is often amplified and overexpressed in cancer. Here we model HLTF dysregulation through the functionally conserved Saccharomyces cerevisiae ortholog, RAD5. Genetic interaction profiling and landscape enrichment analysis of RAD5 overexpression (RAD5OE) reveals requirements for genes involved in recombination, crossover resolution, and DNA replication. While RAD5OE and rad5Δ both cause cisplatin sensitivity and share many genetic interactions, RAD5OE specifically requires crossover resolving genes and drives recombination in a region of repetitive DNA. Remarkably, RAD5OE induced recombination does not require other post-replication repair pathway members, or the PCNA modification sites involved in regulation of this pathway. Instead, the RAD5OE phenotype depends on a conserved domain necessary for binding 3' DNA ends. Analysis of DNA replication intermediates supports a model in which dysregulated Rad5 causes aberrant template switching at replication forks. The direct effect of Rad5 on replication forks in vivo, increased recombination, and cisplatin sensitivity predicts similar consequences for dysregulated HLTF in cancer.

Increased chromosomal mobility after DNA damage is controlled by interactions between the recombination machinery and the checkpoint

In this study, Smith et al. investigated how cells modulate chromosome mobility in response to DNA damage. They show that global chromosome mobility is regulated by the Rad51 recombinase and its mediator, Rad52, and their findings indicate that interplay between recombination factors and the checkpoint restricts increased mobility until recombination proteins are assembled at damaged sites.

During homologous recombination, cells must coordinate repair, DNA damage checkpoint signaling, and movement of chromosomal loci to facilitate homology search. In Saccharomyces cerevisiae, increased movement of damaged loci (local mobility) and undamaged loci (global mobility) precedes homolog pairing in mitotic cells. How cells modulate chromosome mobility in response to DNA damage remains unclear. Here, we demonstrate that global chromosome mobility is regulated by the Rad51 recombinase and its mediator, Rad52. Surprisingly, rad51Δ rad52Δ cells display checkpoint-dependent constitutively increased mobility, indicating that a regulatory circuit exists between recombination and checkpoint machineries to govern chromosomal mobility. We found that the requirement for Rad51 in this circuit is distinct from its role in recombination and that interaction with Rad52 is necessary to alleviate inhibition imposed by mediator recruitment to ssDNA. Thus, interplay between recombination factors and the checkpoint restricts increased mobility until recombination proteins are assembled at damaged sites.

CRISPR-Mediated Base Editing Enables Efficient Disruption of Eukaryotic Genes through Induction of STOP Codons

Standard CRISPR-mediated gene disruption strategies rely on Cas9-induced DNA double-strand breaks (DSBs). Here, we show that CRISPR-dependent base editing efficiently inactivates genes by precisely converting four codons (CAA, CAG, CGA, and TGG) into STOP codons without DSB formation. To facilitate gene inactivation by induction of STOP codons (iSTOP), we provide access to a database of over 3.4 million single guide RNAs (sgRNAs) for iSTOP (sgSTOPs) targeting 97%-99% of genes in eight eukaryotic species, and we describe a restriction fragment length polymorphism (RFLP) assay that allows the rapid detection of iSTOP-mediated editing in cell populations and clones. To simplify the selection of sgSTOPs, our resource includes annotations for off-target propensity, percentage of isoforms targeted, prediction of nonsense-mediated decay, and restriction enzymes for RFLP analysis. Additionally, our database includes sgSTOPs that could be employed to precisely model over 32,000 cancer-associated nonsense mutations. Altogether, this work provides a comprehensive resource for DSB-free gene disruption by iSTOP.

Utilization and expenditures for ambulatory medical care by people hospitalized: United States, 1980

The National Medical Care Utilization and Expenditure Survey was conducted throughout 1980 to collect information on health, access to and use of medical services, associated charges and sources of payment, and health insurance coverage. The survey was based on a probability sample of about 6,600 households and 17,123 people representative of the civilian noninstitutionalized population of the United States. This report is one of a series of descriptive reports based on data from the National Medical Care Utilization and Expenditure Survey. It characterizes the population by hospital utilization and certain sociodemographic and health variables, and shows how hospitalization effects the use and cost of ambulatory medical care. The following are some of the highlights of the report. Almost everyone was covered by some form of health insurance at some time during 1980. Only 7.6 percent were not covered at all, and 10 percent had insurance only part of the year. The proportion not covered at all varied according to the number of times hospitalized, ranging from 8.2 percent for people not hospitalized during the year to 1.8 percent for people hospitalized three or more times. People with one or more hospital stays during 1980 had a physician visit rate greater than three times that for people not hospitalized. Similarly, the expenditures for ambulatory medical care for people experiencing hospitalizations was almost nine times that for people were not hospitalized during the year. The rate of physician visits is much larger immediately prior to hospital admission or immediately after discharge than it is at other times. About 40 percent of all physician visits during the year occurred within a month before admission and after discharge. within a month before admission and after discharge.

Graduate follow-up in the US Air Force family practice residency programs

Between June 30, 1973, and June 30, 1982, 216 family physicians completed residency training in family practice residencies sponsored by the US Air Force. The primary purpose of this study was to measure the adequacy of the graduates' residency training program. One hundred seventy-nine (83 percent) of the graduates responded to an extensive eight-page survey. The study assessed all Air Force program graduates as a whole as well as each program separately. Seventy-four percent of the respondents are still in the Air Force. All but one are board certified, and 19 have been recertified. Of the 179 respondents, 37.0 percent are involved in teaching medical students of family practice residents, only 5.0 percent are dissatisfied with their present hospital privileges, 43.5 percent felt that their residency training was superior to that provided by civilian family practice residency, 53.7 percent felt the training was equal, and 2.8 percent felt the training was inferior. Practice satisfaction and continuing medical education needs were also addressed in the study.

Sample design and estimation procedures for a national health examination survey of children

The Health Examination Survey is one of the major survey programs employed by the National Center for Health Statistics to obtain information about the health status of the U.S. population. It is a part of the National Health Survey, authorized in 1956 by the 84th Congress as a continuing Public Health Service activity. The National Health Survey employs three different survey programs to accomplish its objectives. One of these is the Health Interview Survey in which persons are asked to give in-formation related to their health or to the health of other household members. The second program, Health Resources, obtains health data and health resource and utilization information through surveys of hospitals, nursing homes, and other resident institutions and through the entire range of personnel in the health occupations. The third major program is the Health Examination Survey (HES), The Health Examination Survey collects data from samples of the civilian, noninstitutional population of the United States and, by means of medical and dental examinations and various tests and measurements, undertakes to characterize the population under study. This is the most accurate way to obtain diagnostic data on the prevalence of certain medically defined illnesses. It is the only way to obtain information on unrecognized and undiagnosed conditions-in some cases, even nonsymptomatic conditions. It is also the only way presently available to obtain distributions of the population by a variety of physical, physiological, and psychological measurements. Although the sample is designed primarily to estimate the prevalence of specified health and health-related conditions in the population, the design also makes possible the study of relationships of the examination findings to one another and to certain demographic and socioeconomic factors.