Known Roles of RNA in Cells Today provides supporting evidence for an RNA World Concept.         besides the traditional roles of   mRNA,    rRNA,    tRNA...

1.  some RNAs self splice introns in protozoans, mitochondria,  & some chloroplasts...                (most intron splicing is done by splicesomes, but some introns self-splice)   2.  Viroids - are infectious RNA molecules of plants w/o protein coats...    3.  primer RNA molecules, which are needed during DNA replication...   4.  small RNA molecules have numerous functions:               U-rich RNA in splicesomes,  micro-RNAs transcription interference,               telomerase-RNA component replicates DNA ends,   5.  riboswitches - RNA motifs that bind to small molecules & change their conformations   6.  Peptidyl transferase - a ribozyme that form peptide bonds in cells.    --> some lab have made artificial RNAs can be selected for ligase activity         & experimentally mutated...       back                               *