A free cytoplasmic 22 S ribonucleoprotein particle exhibiting a major template activity in rabbit reticulocyte system has been identified in the cryptobiotic gastrulae of Artemia salina. This particle contains non-polyadenylated 9 S messenger RNA which codes primarily for a non-histone basic protein with an apparent molecular weight of 26 000 daltons. We have previously demonstrated the presenc...

RNase MRP is a site-specific ribonucleoprotein endoribonuclease that processes RNA from the mammalian mitochondrial displacement loop containing region. RNase P is a site-specific ribonucleoprotein endoribonuclease that processes pre-tRNAs to generate their mature 5'-ends. A similar structure for the RNase P and RNase MRP RNAs and a common cleavage mechanism for RNase MRP and RNase P enzymes ha...

The induction of autoantibodies to U1 small nuclear ribonucleoprotein (U1 snRNP) complexes is not well understood. We present evidence that healthy individuals with cytomegalovirus (CMV) infection have an increased frequency and quantity of antibodies to ribonucleoprotein, directed primarily against the U1-70k protein. A significant association between the presence of antibodies to CMV and anti...

Mature ribosomes, their subunits, and their ribonucleoprotein precursors were extracted from HeLa cells and prepared for electron microscopy by a method based on adsorption of nucleic acid to a charged grid. Images so obtained revealed the presence of two types of ribonuclease-sensitive fibrils of consistent morphology. One of these types of fibril is present on the 80S and 55S nucleolar ribonu...

RNase P is an essential enzyme that cleaves the 5' leader sequence of tRNA precursors. RNase Ps were believed until now to occur universally as ribonucleoproteins in organisms performing RNase P activity. Here we find that protein-only RNase P enzymes called PRORP (for proteinaceous RNase P) support RNase P activity in vivo in both organelles and the nucleus in Arabidopsis. Beyond tRNA, PRORP p...

RNase P is the enzyme that removes 5' leader sequences from precursor tRNAs. Remarkably, in most organisms, RNase P is a ribonucleoprotein particle where the RNA component is responsible for catalysis. In this issue of Genes & Development, Gutmann and colleagues (pp. 1022-1027) report the first organism, Arabidopsis thaliana, to employ protein-only RNase P in both its nucleus and organelles. An...