FIG. 8.

Model of the role of RNase MRP in cell cycle control. Based on our results, RNase MRP is responsible for degradation of the CLB2 mRNA. This is accomplished by processing the CLB2 mRNA in its 5′-UTR, resulting in an uncapped transcript. This uncapped transcript is then efficiently degraded by the Xrn1 5′-3′ exoribonuclease. Defects in RNase MRP increase levels of the CLB2 mRNA, producing more Clb2 protein. Sustained levels of Clb2 protein keep the cyclin-dependent kinase Cdc28 active and inhibit the end of mitosis. Genetic interactions between RNase MRP and the exit from the mitosis pathway may indicate potential regulation points of RNase MRP or a bypass involving activation of the Clb2 protein degradation pathway (4).