Host factor for coliphage Qbeta RNA replication is present in Pseudomonas putida.

Host Factor (HF)1, is a 12000 molecular weight polypeptide that is found in uninfected Escherichia coli and is required as a hexamer along with Qbeta replicase for in vitro replication of Qbeta phage RNA. It has recently been found to be associated with ribosomes and to bind tightly to poly(A). We report here the identification and purification of HF from Pseudomonas putida. HF can be detected in crude extracts by both functional activity in the Qbeta RNA replication assay and by immunodiffusion with antibody made against E. coli HF. HF from E. coli and P. putida chromatograph similarly on DEAE-cellulose and phosphocellulose. They have similar but not identical molecular weights as judged by SES-polyacrylamide gel electrophoresis. Like E. coli HF, P. putida HF was found to be associated with ribosomes and to bind tightly to poly(A). Furthermore, the pure protein from P. putida has full funcitonal activity in the in vitro Qbeta RNA replication assay. The findings that HF has been conserved during evolution, is associated with ribosomes, and binds poly(A), suggest that HF may be an important translational element in uninfected cells and that its role involves an interaction with RNA.