A Sequence of 83 Nucleotides Containing the Replicase Cistron Ribosome Binding Site of Phage Qbeta RNA

70-S initiation complexes of Escherichia coli ribosomes and 32P-labelled Qβ RNA were digested with T1 ribonuclease at 0°C, and the ribosome-protected Qβ initiator fragments resolved by poly-acrylamide gel electrophoresis. The sequence of one of the fragments (83 nucleotides long) has been determined. It begins with the sequence of 32 nucleotides already determined for the ribosome binding site of the replicase cistron. The sequence of the remaining 51 nucleotides establishes the order of a further 17 amino acids in the phage-coded replicase subunit. Seven out of the first 11 amino acids in the replicase subunits of phages MS2 and Qβ are identical.