ESCHERICHIA-COLI RIBOSOMAL-PROTEIN L3 STIMULATES THE HELICASE ACTIVITY OF THE BACILLUS-STEAROTHERMOPHILUS PCRA HELICASE

Escherichia coil ribosomal protein L3 stimulates the in vitro helicase activity of Bacillus stearothermophilus PcrA helicase upon a variety of different substrates. L3 has no intrinsic helicase or ATPase activi ty nor is it able to stimulate the ATPase activity of PcrA. Gel mobili ty shift assays revealed that the affinity of PcrA for a variety of di fferent DNA species (single-stranded, nicked and 3'-tailed) was enhanc ed in the presence of L3. We suggest that the stimulatory effect of L3 upon the helicase activity of PcrA is mediated via a protein-protein interaction which promotes cooperative binding of PcrA to its DNA subs trate. This activity of L3 appears to be specific for PcrA helicase.