Tight Regulation of Srs2 Helicase Activity Is Crucial for Proper Functioning of DNA Repair Mechanisms

Proper DNA damage repair is one of the most vital and fundamental functions of every cell. Several different repair mechanisms exist to deal with various types of DNA damage, in various stages of the cell cycle and under different conditions. Homologous recombination is one of the most important repair mechanisms in all organisms. Srs2, a regulator of homologous recombination, is a DNA helicase involved in DNA repair, cell cycle progression and genome integrity. Srs2 can remove Rad51 from ssDNA, and is thought to inhibit unscheduled recombination. However, Srs2 has to be precisely regulated, as failure to do so is toxic and can lead to cell death. We noticed that a very slight elevation of the levels of Srs2 (by addition of a single extra copy of the SRS2 gene) leads to hyper-sensitivity of yeast cells to methyl methanesulfonate (MMS, a DNA damaging agent). This effect is seen in haploid, but not in diploid, cells. We analyzed the mechanism that controls haploid/diploid sensitivity and arrived to the conclusion that the sensitivity requires the activity of RAD59 and RDH54, whose expression in diploid cells is repressed. We carried out a mutational analysis of Srs2 to determine the regions of the protein required for the sensitization to genotoxins. Interestingly, Srs2 needs the HR machinery and its helicase activity for its toxicity, but does not need to dismantle Rad51. Our work underscores the tight regulation that is required on the levels of Srs2 activity, and the fact that Srs2 helicase activity plays a more central role in DNA repair than the ability of Srs2 to dismantle Rad51 filaments

Platelet-Rich Plasma for Knee Osteoarthritis: Internet Marketing and Patient Education—An Appraisal of Content for Websites with the Greatest Search Engine Visibility

Objective The internet is increasingly being used as a resource for health-related information by the general public. We sought to establish the authorship, content, and accuracy of the information available online regarding platelet-rich plasma (PRP) therapy for knee osteoarthritis. Design Top 200 search results from each of the 3 leading search engines available online (Google, Yahoo!, Bing) were screened, and 181 websites were finally reviewed for content with emphasis on specific claims, comparing between websites authored by private physicians/groups and other authorship types. Results Nearly 80% of the websites claimed that PRP injections for osteoarthritis of the knee improve patients’ pain. A total of 42.8% of the private websites and 27.6% of nonprivate websites have stated that the procedure can delay or eliminate the need for future surgery. Costs were only mentioned by few (11.6%), and mainly by the nonprivate websites. Both website groups were unlikely to mention that PRP therapy is not the treatment of choice for end-stage knee osteoarthritis (7.9% of private and 17.2% of the nonprivate sites), or to state that patients with less advanced disease may benefit more from the treatment (11.8% and 20.6%, respectively). Private websites were less likely to refer to peer-reviewed literature (18.4% vs. 41.4%) and were more than 3 times less likely to mention lack of adequate evidence (13.2% vs. 48.2%). Conclusions Patients seeking online information regarding PRP therapy are vulnerable to websites presenting a narrow viewpoint of this treatment modality, putting emphasis on unsubstantiated benefits while disregarding potential drawbacks and concerns