MAPPING OF MUTATIONS CONTRIBUTING TO THE TEMPERATURE SENSITIVITY OF THE SABIN-1 VACCINE STRAIN OF POLIOVIRUS

The temperature-sensitive and attenuated phenotypes of the Sabin type 1 vaccine strain of poliovirus result from numerous point mutations wh ich occurred in the virulent Mahoney virus parent. One of these mutati ons is located in a 3D polymerase (3D(Pol)) codon (U-6203-->C, Tyr 73- ->His) and is involved in attenuation in common mice (M. Tardy-Panit, B. Blondel, A. Martin, F. Tekaia, F. Horaud, and F. Delpeyroux, J. Vir ol. 67:4630-4638, 1993). This mutation also appears to contribute to t emperature sensitivity in association with at least 1 other of the 10 mutations of the 3'-terminal part of the genome including the 3D(Pol) coding and 3' noncoding regions. To map the other mutation(s), we cons tructed poliovirus mutants by mutagenesis and recombination of Mahoney and Sabin 1 cDNAs. Characterization of these poliovirus mutants showe d that a second mutation in a 3D(Pol) codon (C-7071-->U, Thr-362-->Ile ) contributes to temperature sensitivity. A mutation in the 3' noncodi ng region of the genome (A-7441-->G), alone or linked to another mutat ion (U-7410-->C), also appeared to be involved in this phenotype. The temperature-sensitive effect associated with the 3'-terminal part of t he Sabin 1 genome results from the cumulative and/or synergistic effec ts of at least three genetic determinants, i.e., the His-73 and Ile-36 2 codons of 3D(Pol) and nucleotide G-7441. Sequence analysis of strain s isolated from patients with vaccine-associated paralytic poliomyelit is showed that these genetic determinants are selected against in vivo , although the Ile-362 codon appeared to be more stable than either th e His-73 codon or G-7441. These genetic determinants may contribute to the safety of Sabin 1 in vaccinees.