Regulating the regulators: How ribonucleases dictate the rules in the control of small non-coding RNAs

Gene regulation was long thought to be controlled almost entirely by proteins that bind to DNA and RNA. Over the last years, it has become clear that small non-coding RNAs (sRNAs) are important in almost every facet of gene regulation. Understanding how they are matured and degraded has therefore become of maximum importance, in order to know how to "regulate the regulators." Ribonucleases perform a key role in the biogenesis and processing of sRNAs, as well as in controlling their cellular levels through regulation of their turnover. Accordingly, RNases can have a major impact on sRNAs regulatory pathways. In this review, we present an overview of what is presently known about the main RNases, as well as other factors involved in sRNA processing and turnover, in essence contributing to the assembly of the increasing number of pieces in the puzzling global mechanism of sRNA regulation. Although the primary focus will be on bacterial sRNAs, parallels will be made with the siRNAs and miRNAs in eukaryotes.