Genetic 'Fossils' Reveal Long-Term Viral Partnerships in Grass (image) PLOS Share Print E-Mail Caption To complete the life cycles, defective pararetrovirus species have evolved to form partnerships which are maintained by frequent exchanges of their noncoding regulatory sequences (NRSs). Credit Sunlu Chen & Yuji Kishima Usage Restrictions All figures and photographic images will be published under a Creative Commons Attribution License (CCAL), which allows them to be freely used, distributed, and built upon as long as proper attribution is given. Share Print E-Mail Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.