Abstract
In this chapter, we will present that RNA molecules are more than just messengers between genes and proteins. The human genome is extensively transcribed also outside protein coding regions giving rise to tens of thousands of ncRNAs. Not all of these transcripts are functional, however, many ncRNAs have regulatory specificity, i.e., some of them function similarly to proteins. For example, miRNAs are small ncRNAs that regulate posttranscriptionally the expression of several thousand genes. They share many similarities together with transcription factors and therefore are useful for different regulatory processes. The most effective targets of miRNAs are members of signal transduction cascades, such as receptors, kinases and transcription factors. Long ncRNAs have a number of mechanisms available to regulate biological processes, such as the initiation of the imprinting process XCI via Xist . A special variant of long ncRNAs are eRNAs that are produced bidirectionally at enhancer regions, when the latter interact with promoter regions.