Y？RNAs constitute a family of highly conserved small noncoding RNAs (in humans: 83-112 nt; Y1, Y3, Y4 and Y5). They are transcribed from individual genes by RNA-polymerase？III and fold into conserved stem-loop-structures. Although discovered 30 years ago, insights into the cellular and physiological role of Y？RNAs remains incomplete. In this review, we will discuss knowledge on the structural properties, associated proteins and discuss proposed functions of Y？RNAs. We suggest Y？RNAs to be an integral part of ribonucleoprotein networks within cells and could therefore have substantial influence on many different cellular processes. Putative functions of Y？RNAs include small RNA quality control, DNA replication, regulation of the cellular stress response and proliferation. This suggests Y？RNAs as essential regulators of cell fate and indicates future avenues of research, which will provide novel insights into the role of small noncoding RNAs in gene expression.
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