THE BACTERIOPHAGE-T4 REGB RIBONUCLEASE - STIMULATION OF THE PURIFIED ENZYME BY RIBOSOMAL-PROTEIN-S1

Infection of Escherichia coil by bacteriophage T4 induces a mRNA ribon uclease activity that shows specificity for cleavage within the sequen ce GGAG. Substrates of the activity in vivo include a number of phage mRNAs that are cleaved at GGAGs within the Shine/Dalgarno domains of t heir translation initiation regions. Induction of the ribonuclease dep ends on the product of the T4 gene regB. We describe here the overprod uction and extensive purification of the RegB protein. RegB precisely co-purifies with an activity that cleaves within the sequence GGAG in oligonucleotide and polynucleotide RNAs and is therefore likely to con stitute the sequence-specific catalytic component of the observed acti vity. We further report that the low cleavage rate observed with our p reparations of purified RegB is substantially increased (1-2 orders of magnitude) by the addition of E. coil ribosomal protein S1. We discus s the implications of this observation for the mechanism of action of the RegB ribonuclease in vitro and in vivo.