IN-VITRO SELECTION OF RNA SPECIFICALLY CLEAVED BY BACTERIOPHAGE-T4 REGB ENDONUCLEASE

T4 RegB endonuclease specifically cleaves at -GGAG- sites in several e arly T4 messages, rendering them nonfunctional. Not all -GGAG- sites a re processed equally by RegB; those found at the Shine-Dalgarno sequen ces and in intercistronic regions are processed with higher efficiency than the -GGAG- sites located in coding regions. The low activity of RegB observed in vitro is enhanced by 1-2 orders of magnitude by the E scherichia coli ribosomal protein S1. We have used SELEX (systematic e volution of ligands by exponential enrichment) on a combinatorial RNA library to obtain molecules that are specifically cleaved by T4 RegB e ndonuclease in the presence of S1. The sequences obtained contain the required -GGAG- tetranucleotide and were unusually enriched in adenosi ne and cytosine nucleotides. No consensus structure or sequence motif other than -GGAG- was conserved among the selected molecules. The majo rity of the RNAs are entirely dependent on S1 for RegB-catalyzed cleav age; however, a few RNAs are found to be S1 independent but are cleave d by RegB with much lower rates.