23 April 2020

Knowledge of the molecular events in mitochondrial DNA (mtDNA) replication is crucial to understanding the origins of human disorders arising from mitochondrial dysfunction. Twinkle helicase is an essential component of mtDNA replication. Here, we employed atomic force microscopy imaging in air and liquids to visualize ring assembly, DNA binding, and unwinding activity of individual Twinkle hexamers at the single-molecule level. We observed that the Twinkle subunits self-assemble into hexamers and higher-order complexes that can switch between open and closed-ring configurations in the absence of DNA. Our analyses helped visualize Twinkle loading onto and unloading from DNA in an open-ringed configuration. They also revealed that closed-ring conformers bind and unwind several hundred base pairs of duplex DNA at an average rate of ∼240 bp/min. We found that the addition of mitochondrial single-stranded (ss) DNA–binding protein both influences the ways Twinkle loads onto defined DNA substrates and stabilizes the unwound ssDNA product, resulting in a ∼5-fold stimulation of the apparent DNA-unwinding rate. Mitochondrial ssDNA-binding protein also increased the estimated translocation processivity from 1750 to >9000 bp before helicase disassociation, suggesting that more than half of the mitochondrial genome could be unwound by Twinkle during a single DNA-binding event. The strategies used in this work provide a new platform to examine Twinkle disease variants and the core mtDNA replication machinery. They also offer an enhanced framework to investigate molecular mechanisms underlying deletion and depletion of the mitochondrial genome as observed in mitochondrial diseases.

In bacteria, the restart of stalled DNA replication forks requires the DNA helicase PriA. PriA can recognize and remodel abandoned DNA replication forks, unwind DNA in the 3'-to-5' direction, and facilitate the loading of the helicase DnaB onto the DNA to restart replication. Single-stranded DNA–binding protein (SSB) is typically present at the abandoned forks, but it is unclear how SSB and PriA interact, although it has been shown that the two proteins interact both physically and functionally. Here, we used atomic force microscopy to visualize the interaction of PriA with DNA substrates with or without SSB. These experiments were done in the absence of ATP to delineate the substrate recognition pattern of PriA before its ATP-catalyzed DNA-unwinding reaction. These analyses revealed that in the absence of SSB, PriA binds preferentially to a fork substrate with a gap in the leading strand. Such a preference has not been observed for 5'- and 3'-tailed duplexes, suggesting that it is the fork structure that plays an essential role in PriA's selection of DNA substrates. Furthermore, we found that in the absence of SSB, PriA binds exclusively to the fork regions of the DNA substrates. In contrast, fork-bound SSB loads PriA onto the duplex DNA arms of forks, suggesting a remodeling of PriA by SSB. We also demonstrate that the remodeling of PriA requires a functional C-terminal domain of SSB. In summary, our atomic force microscopy analyses reveal key details in the interactions between PriA and stalled DNA replication forks with or without SSB.

Histone H2B monoubiquitylation (H2Bub1) has central functions in multiple DNA-templated processes, including gene transcription, DNA repair, and replication. H2Bub1 also is required for the trans-histone regulation of H3K4 and H3K79 methylation. Although previous studies have elucidated the basic mechanisms that establish and remove H2Bub1, we have only an incomplete understanding of how H2Bub1 is regulated. We report here that the histone H4 basic patch regulates H2Bub1. Yeast cells with arginine-to-alanine mutations in the H4 basic patch (H42RA) exhibited a significant loss of global H2Bub1. H42RA mutant yeast strains also displayed chemotoxin sensitivities similar to, but less severe than, strains containing a complete loss of H2Bub1. We found that the H4 basic patch regulates H2Bub1 levels independently of interactions with chromatin remodelers and separately from its regulation of H3K79 methylation. To measure H2B ubiquitylation and deubiquitination kinetics in vivo, we used a rapid and reversible optogenetic tool, the light-inducible nuclear exporter, to control the subcellular location of the H2Bub1 E3 ligase, Bre1. The ability of Bre1 to ubiquitylate H2B was unaffected in the H42RA mutant. In contrast, H2Bub1 deubiquitination by SAGA-associated Ubp8, but not by Ubp10, increased in the H42RA mutant. Consistent with a function for the H4 basic patch in regulating SAGA deubiquitinase activity, we also detected increased SAGA-mediated histone acetylation in H4 basic patch mutants. Our findings uncover that the H4 basic patch has a regulatory function in SAGA-mediated histone modifications.

A discussion featuring data on immigration trends and the agricultural workforce, and some of the adjustments that farm employers are making, including increased mechanization, improved wages and benefits, and the increased use of the H-2A program. University of California-Davis’s Phil Martin, along with researchers from the the U.S. Department of Agriculture, U.S. Department of Labor, present their findings on the foreign agricultural workforce in the United States, which is followed by comments from the President of Farmworker Justice on some of the policy implications.

Amid ongoing Brexit negotiations, much remains uncertain for the roughly 1 million UK citizens living elsewhere in the European Union. This report offers a demographic profile of these Brexpats, considering what form an EU-UK deal on citizens’ rights might take and identifying key challenges many Britons are likely to face—including difficulty securing legal status and accessing labor markets, social security, and health-care systems.

With immigration increasingly visible in the news and the political space in the United States and internationally, getting access to accurate, high-quality data is essential to understand immigration’s demographic effects and impacts on the economy, education and labor systems, and communities. This event marks the release of the Immigration Data Matters guide.

Where can you find the most accurate statistics on some of the top immigration issues—ranging from the size of immigrant and emigrant populations, to humanitarian and labor flows, naturalization rates, enforcement statistics, remittances, and more? In this brief video, Jeanne Batalova, who manages the Migration Policy Institute’s Migration Data Hub, walks you through the Immigration Data Matters guide developed by MPI and the Population Reference Bureau.
 

Marking the release of MPI President Andrew Selee's latest book, speakers explore emerging trends in migration, economic interdependence, technology innovation, and cultural exchange that are transforming the relationship between the United States and Mexico, and the policy implications of these changes for the future.

Even as the 1.8 million number swirls in the discussion of how many DREAMers would be placed on a path to citizenship, proposals debated in the Senate in February 2018 would have resulted in the legalization of smaller numbers, as this commentary explains. It offers estimates of potential beneficiaries of several Senate proposals, including one backed by the White House, and analysis of key criteria.

A report release and presentation of first-ever U.S. estimates on the actual economic costs of skill underutilization for immigrants, their families, and the U.S. economy, in terms of forgone earnings and unrealized federal, state, and local taxes.

More than 1 million international students were in the United States in 2015-16, a significant share of them in science, technology, engineering, or math (STEM) fields. While countries increasingly are vying for this population, these individuals face a complex choice upon graduation: to stay or leave? This article examines international STEM students in the United States and the motivations underlying their postgraduation plans.

Over the past decade, immigrant investor programs have proliferated around the world, and Chinese applicants have dominated in a number of countries. In 2015, about 9,000 Chinese millionaires moved to other countries, many through so-called golden visa programs. This article explores the social and cultural factors driving well-off Chinese to move abroad and examines perceptions of elite emigration in China.

During its first year, the Trump administration methodically put in place a series of bureaucratic barriers that could significantly reduce opportunities for foreigners to come to the United States legally. Among the actions taken during 2017: Imposition of a much-challenged travel ban suspending the entry of nationals from certain Muslim-majority countries, cuts to refugee admissions, and increased scrutiny for visa applicants.

At this release of an updated version of the popular Immigration Data Matters guide, presenters discuss how to navigate and access the increasing number of data sources on immigration and immigrants in the United States and internationally. 

Faced with a lack of employment opportunities and recurrent poverty, Albanian youth migrate to Italy alone in the hopes of improving their educational prospects or making money for their families. Yet upon arrival, they face many vulnerabilities. While some protections for unaccompanied minors exist in the Italy, the system is greatly fragmented and challenges, including how to return them to Albania, remain persistent.

The Trump administration’s decision to terminate the Deferred Action for Childhood Arrivals (DACA) deportation-relief program launched in 2012 has sparked new urgency to find a longer-term fix for "DREAMers," the unauthorized immigrants brought to the United States as children. This Policy Beat article examines movement in the courts and in Congress on the DREAM Act and similar proposals, exploring likely paths forward.

In its first year, the Trump administration moved to deliver on some of Donald Trump’s campaign promises on immigration, including ramping up enforcement in the U.S. interior and ending the Deferred Action for Childhood Arrivals (DACA) program. The administration also announced the termination of Temporary Protected Status (TPS) for nationals of some countries. This article explores some of the top policy changes.

Experts on this Spanish language webinar examine the operation of today’s interior immigration enforcement system and how state and local governments, civil society, and consulates are responding.    

Remain in Mexico—the Trump administration policy aimed at deterring the rising numbers of migrants from Central America by requiring them to stay in Mexico through most of their U.S. asylum adjudication process—bears striking similarities to U.S. policy in the 1980s and 1990s that sought to discourage Haitians from making the sea journey to the United States. This article explores the parallels and differences between Remain in Mexico and the earlier narrowing of asylum for Haitians.

The immigrant population in the Kansas City region has grown rapidly over the past 25 years, contributing to overall population growth in the area. This fact sheet describes immigrants in the metro area, examining their origins, industries of employment, income and poverty levels, English proficiency, educational attainment, and more.

Citizenship and integration policies are often thought of as markers for whether a country is welcoming to immigrants. Yet research suggests that public opinion and political rhetoric play a bigger role in immigrants' sense of belonging. This article explores how boundaries between "us" and "them" are drawn through popular conceptions of nationhood and political rhetoric, and their impact on immigrants' belonging.

This report analyzes the exploitation of migrants in three spheres: the domestic care sector, the labor market, and the sex industry. It details several obstacles governments face in their efforts to weaken the "bad actors" that profit from exploitation, and shows how one of the biggest challenges facing law enforcement is that serious criminals and lawbreakers often operate on the edge of legality and exploit legal routes wherever possible.

A Spanish language webinar examining the operation of today’s interior enforcement system and how state and local governments, civil society, and consulates are responding.    

China has been Africa’s largest trading partner since 2009, and as commerce and investment have increased, so have flows of people in both directions. With an estimated 1 million to 2 million Chinese migrants across Africa, some countries have relaxed their short-term visa requirements in hopes of facilitating cultural and business exchanges. High levels of Chinese investment do not, however, correlate with more liberal visa policies, as this article explores.

With more than 3 million Venezuelans having fled their country in crisis, this event features the release of an MPI-OAS report that examines the creative responses that host countries in Latin America are providing. These include the opening of legal pathways to residence, access to formal labor markets, and greater use of forms of ID for recognition.

With many countries in East Asia facing unfavorable demographic shifts in the form of aging populations, low fertility, and shrinking workforces, governments in 2016 continued to explore immigration as a potential policy solution. However, a tradition of cultural homogeneity and wariness among publics about increased immigration is leading policymakers to test the waters with very small steps.

This event focuses on the changing face of Mexican migration to the United States, Mexican immigrants' contributions to U.S. society and political and economic power, as well as that of those who have returned to Mexico.

In his first public address on his inaugural official visit to Washington, DC, IOM Director General António Vitorino discusses his vision for IOM; reforms in the UN system; coordination with other organizations in addressing humanitarian protection; and the operational steps IOM is taking to respond to forced migration and displacement.

Bangladeshis in 2017 suddenly emerged as one of the top migrant groups entering Europe illegally. While Europe is a new destination, Bangladeshi labor migration has been an important part of the country's development since the 1970s, with growing numbers heading abroad, largely to the Gulf Cooperation Council countries. This article explores and contextualizes the new phenomenon of Bangladeshi migration to Europe.

Although in many countries immigrants fill labor gaps in fields such as agriculture and construction, few legal migration pathways exist for low-skilled workers. As states meet to negotiate a Global Compact for Safe, Orderly, and Regular Migration, this policy brief takes stock of the channels available for such workers to move legally and take up work abroad, highlighting promising practices and policy gaps.

As policymakers look for ways to address the drivers of illegal immigration, many have called for migration aims to be incorporated into development work and development tools into migration partnerships. This policy brief analyzes the benefits and risks of heightened cooperation between actors in these fields, and identifies areas where joint initiatives may prove fruitful.

One of the least developed countries in sub-Saharan Africa, the Democratic Republic of the Congo has experienced significant migration outflows and inflows tied to political and economic crises in recent decades. While most Congolese migrants head to neighboring countries, destinations have diversified, with an uptick in those leaving for opportunities in Europe and beyond. This country profile explores historical and contemporary patterns of migration to and from DR Congo.