Noncoding RNAs: persistent viral agents as modular tools for cellular needs.

It appears that all the detailed steps of evolution stored in DNA that are read, transcribed, and translated in every developmental and growth process of each individual cell depend on RNA-mediated processes, in most cases interconnected with other RNAs and their associated protein complexes and functions in a strict hierarchy of temporal and spatial steps. Life could not function without the key agents of DNA replication, namely mRNA, tRNA, and rRNA. Not only rRNA, but also tRNA and the processing of the primary transcript into the pre-mRNA and the mature mRNA are clearly descended from retro-"elements" with obvious retroviral ancestry. They seem to be remnants of viral infection events that did not kill their host but transferred phenotypic competences to their host and changed both the genetic identity of the host organism and the identity of the former infectious viral swarms. In this respect, noncoding RNAs may represent a great variety of modular tools for cellular needs that are derived from persistent nonlytic viral settlers.