%0 Journal Article %A Oxford, J. S. %A Corcoran, T. %A Schild, G. C. %T Naturally Occurring Temperature-sensitive Influenza A Viruses of the H1N1 and H3N2 Subtypes %D 1980 %J Journal of General Virology, %V 48 %N 2 %P 383-389 %@ 1465-2099 %R https://doi.org/10.1099/0022-1317-48-2-383 %I Microbiology Society, %X SUMMARY Seventeen of twenty-six influenza A virus isolates of the H1N1 antigenic subtype and two of eleven H3N2 virus isolates from the 1977–78 season exhibited a ts phenotype, were restricted in plaquing in MDCK cells at 38.5 °C compared to 34 °C and appeared to be naturally occurring ts mutants. The cut-off temperature for two such ts H1N1 virus isolates was established as 38 °C. The ts viruses were as thermostable as non-ts isolates and no complementation was detected between the twelve ts viruses tested. Cloning studies with an H1N1 virus isolate with minimal ts properties indicated the presence of a mixed population of ts + and ts particles. Analysis of seven recombinants of A/HK/117/77 (N1N1) virus indicated that the ts lesion(s) was not located in the NA or HA proteins. %U https://www.microbiologyresearch.org/content/journal/jgv/10.1099/0022-1317-48-2-383