Noncoding RNAs in gene regulation.

RNAs have been traditionally viewed as intermediates between DNA and proteins. However, there is a growing body of literature indicating that noncoding RNAs (ncRNAs) are key players for gene regulation, genome stability, and chromatin modification. In addition to the well-known small interfering RNAs and microRNAs acting in transcriptional and posttranscriptional gene silencing, recent advances in the field of transcriptome exploration have revealed novel sets of new small and large ncRNAs. Many of them appear to be conserved across mammals, and abnormal expression of several ncRNAs has been linked to a wide variety of human diseases, such as cancer. Here, we review the different classes of ncRNAs identified to date, in yeast and mammals, and we discuss the mechanisms by which they affect gene regulation.