Why do mitochondria retain their own genome

first_imgIt sounds like science fiction to suggest that every cell in the human body is occupied by a tiny genome-equipped organelle, with which we exist in symbiosis. But in actuality, eukaryotic life is dependent on mitochondria, which provide energy to the cell in the form of adenosine triphosphate (ATP). Over millennia, the genomes of mitochondria evolved under selection for minimal gene content, but researchers have been unable to determine why some but not all mitochondrial genes have been transferred to the nuclear genome. An international collaborative of researchers formed an interesting hypothesis regarding this phenomenon: The mitochondrial genome encodes hydrophobic membrane proteins which, if encoded in the nucleus, would be filtered by the signal recognition particle (SRP) and misdirected into the endoplasmic reticulum. The researchers conducted a study exploring their hypothesis and have published their results in the Proceedings of the National Academy of Sciences. In order to predict if a protein would be targeted by SRP, the researchers calculated the free insertion energy of transmembrane proteins, which, if scored zero or less, were considered to be hydrophobic. Higher scores were rated marginally hydrophobic. If a transmembrane protein domain (TMD) scored hydrophobic and the length of its tail was longer than 120 amino acids, the researchers predicted it would be arrested by SRP and directed into the endoplasmic reticulum.They expressed such proteins in cellular cytoplasm and were able to determine that they were, in fact, arrested by the SRP and directed to the endoplasmic reticulum. Further, the researchers observed that the mistargeting of these hydrophobic proteins into the soluble medium of the endoplasmic reticulum resulted in the formation of aberrant honeycomb structures similar to those observed during viral infections. “We conclude that genes for hydrophobic membrane proteins of more than 120 amino acids are likely retained in distinct organelle genomes to ensure a correct localization of these proteins and avoid transport to the endoplasmic reticulum,” the authors write.Thus, the researchers conclude, the selection against mistargeting hydrophobic proteins into the endoplasmic reticulum posed at least one major selective constraint on the retention of the mitochondrial genome. They bolster this finding by comparing it to similar membrane dynamics in the chloroplasts of plants.Previous studies have suggested that one-third of mitochondrial proteins have evolved in response to the specific environmental constraints of different species. Most of these proteins are involved with transport, regulatory, and membrane functions. The results of the current study are consistent with these findings. A persistent mystery has been the evidence that in rare cases, transfers of otherwise universal mitochondrial genes into the nuclear genome have occurred. The results of the current study present an explanation: These particular proteins demonstrate reduced hydrophobicity in those species in which the transfer took place.Clinical applications include the development of methods to cure human mitochondrial genetic diseases, such as Leber’s hereditary optic neuropathy. “These results resolve the long-standing question about why aerobic mitochondria and photosynthetic chloroplasts need a distinct compartmental genome, by and large, although other factors may be involved,” the authors write. Journal information: Proceedings of the National Academy of Sciences © 2015 Phys.org This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only. More information: “Mitochondrial genomes are retained by selective constraints on protein targeting.” PNAS 2015 ; published ahead of print July 20, 2015, DOI: 10.1073/pnas.1421372112center_img Mitochondria. Credit: Wikipedia commons Structural data reveals new mechanism behind protein transport Citation: Why do mitochondria retain their own genome? (2015, July 24) retrieved 18 August 2019 from https://phys.org/news/2015-07-mitochondria-retain-genome.html Explore furtherlast_img read more

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Six BusinessFriendly Smartphones That Arent Blackberrys

first_img Blackberry is practically synonymous with business, even as RIM continues to release devices like the Torch in an attempt distance itself from the dull corporate image it has earned over the years.But now the other major players in the smartphone wars — iPhone, Android, and even the new line of Windows Phone 7 devices — are attempting to bite into Blackberry’s enterprise dominance.1. The Dell Venue Pro could prove the Windows Phone 7’s enterprise worthDell already announced that it will be ditching it’s 25,000 company Blackberrys for it’s propriety Windows Phone 7 device.That not only speaks well for the phone, but also the Windows Phone platform as a business tool. What makes this phone stand out among other Windows Phone 7 devices is the sliding QWERTY keyboard, a huge asset for business users.There’s a lot of enterprise potential for Windows Phone 7, and maybe Dell will be the manufacturer to solidify that position.There’s no official announcement on cost yet, but Engadget reports they were told by a Microsoft Store employee that the Venue Pros will be available for $199 with contract.2. The Motorola Droid Pro is a stylish Blackberry killerMotorola took their popular Droid line and reimagined it for the business user.The Droid Pro runs Android 2.2, has a full QWERTY keyboard, and syncs with your company’s e-mail and calendars. It makes a great alternative to the tired look of the Blackberry and has access to the extensive Android Market. The Droid Pro has an expected November 18 release, according to Engadget.Cost: $179.99 with a two-year contract from Verizon.3. iPhone 4 is a contender for enterprise, tooWhen the iPhone first came out in 2007, it was regarded more as a toy than a serious business tool.But now that it has Microsoft Exchange support and thousands of productivity apps, the iPhone is increasingly becoming a viable alternative to the Blackberry.Cost: $199 (16GB) or $299 (32 GB) with a two-year contract from AT&T.4. T-Mobile G2 is a powerful Android optionThe G2’s design and open format make it perfect for the business user who needs some versatility in a smartphone.Engadget calls the G2 one of the purest Android phones available, meaning the OS isn’t bogged down with too much proprietary software or modifications. The design is solid too. It’s almost a clone of the ill-fated Nexus One, but with a slide out QWERTY keyboard for firing off e-mails.Cost: $199.99 with a two-year contract from T-Mobile.5. Samsung FocusIf a physical keyboard doesn’t matter to you and you’re looking for something different, check out one of the other Windows Phone 7 options like the Samsung Focus.The Focus has all the power you’ll need: 1 GHz CPU, Super AMOLED display, and 8 GB of internal storage. Plus the Windows Phone 7 OS makes syncing your Microsoft Office documents, presentations, and Outlook e-mails a snap. As with the Dell Venue Pro, the Samsung Focus has great potential to prove Windows Phone 7’s worth as an enterprise device.Cost: $199.99 with a two-year contract from AT&T.6. The Nokia E5 is unlocked for any networkThis pricey device looks a lot like the Blackberry Bold, but is perfect for the world traveler.Since the Nokia E5 is unlocked, you can avoid being overcharged for an international plan from your U.S. carrier. Slip in a pay-as-you-go SIM card and you’re all set.Cost: $259 from Nokia.Our pick: Dell Venue ProWe think the Windows Phone 7 has serious potential to bridge the gap between enterprise device and fun-to-use smartphone. The initial sale numbers don’t look good, but hopefully we see some more user adoption and useful apps. With luck, RIM will wise up and ditch their clunky Blackberry OS for Windows Phone 7. November 26, 2010 4 min read Brought to you by Business Insider Problem Solvers with Jason Feifer Hear from business owners and CEOs who went through a crippling business problem and came out the other side bigger and stronger. Listen Nowlast_img read more

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