From my text book
The idea of a catalytic role for snRNA arose from the discovery of ribozymes. RNA molecules that function as enzymes. In some organisms, RNA splicing can occur without proteins or additional RNA molecules: The intron RNA functions as a ribozyme and catalyzes its own excision! For example, in the protozoan Tetrahymena, self-splicing occues in the production of ribosomal RNA (rRNA), a component of the organism's ribosomes. The pre-rRna actually removes it's own introns.
The fact that RNA is single stranded plays an important role in allowing certain RNA molecules to function as ribozymes. A region of an RNA molecules may base-pair with a complementary region elsewhere in the same molecules, this imparting specific structure to the RNA molecules as a whole. Also, some of the bases contain functional groups that may participate in catalysis. Just as the specific shape of an enzymatic protein and the functional groups on its amino acid side chains allow the protein to function as a catalyst, the structure of some RNA molecules allows them to function as catalysts too. The discovery of ribozymes rendered obsolete the belief that all biological catalysts were proteins.
RNA processing: RNA splicing. The RNA molecule shown here codes for beta-globin, one of the polypeptides of hemoglobin. the numbers under the RNA reger to codons; beta-globin is 146 amino acids long. the beta-globin gene and its pre-mRNA transcript have three exons, corrresponding to sequences that will leave the nucleus as mRNA. the 5' UTR and 3' UTE are partes of exons because they are included in the mRNAl however, they do not code for protein.) During RNA processing, the introns are cut out and the exons spliced together.
Thomas Cech, of the University of Colorade and Sidney Altman of Yale University found that RYNA, which plays a central role in protein synthesis, can also carry out a number of enzyme-like catalytic functions. Cech called these RNA catalysts Ribozymes. Some ribosymes can make complementary copies of short pieces of RNA, provided that they are supplied with nucleotide building blocks.
a ribozyme capable of replicating RNA. This RNA molecule can make a complementary copy of another piece of RNA (a template_ containing up to 14 nucleotides.
I'm going to go look in another text book of mine and get back to you
