RNASE-P - A SCARLET-PIMPERNEL

RNase P is responsible for the maturation of the 5'-termini of tRNA mo lecules in all cells studied to date. This ribonucleoprotein has to re cognize and identify its cleavage site on a large number of different precursors. This review covers what is currently known about the funct ion of the catalytic subunit of Escherichia coil RNase P, M1 RNA, and the protein subunit, C5, in particular with respect to cleavage-site s election. Recent genetic and biochemical data show that the two C resi dues in the 3'-terminal CCA sequence of a precursor interact with the enzyme through Watson-Crick base-pairing. This is suggested to result in unfolding of the amino acid acceptor-stem and exposure of the cleav age site. Furthermore, other close contact points between M1 RNA and i ts substrate have recently been identified. These data, together with the two existing three-dimensional structure models of M1 RNA in compl ex with its substrate, establish a platform that will enable us to see k an understanding of the underlying mechanism of cleavage by this elu sive enzyme.