Host dependence of naturally occurring temperature-sensitive influenza A viruses and location of their genetic lesions.

Naturally occurring temperature-sensitive (ts) strains have been found in large number in human influenza A viruses of all subtypes (J. Virol. 41 (1982) 353). Further studies have demonstrated that the ts phenotype of these viruses is host-dependent in that they are highly ts in chick embryos and chick embryonic cells, but are ts+ in MDCK cells. Previous studies have located by complementation tests the ts lesion of two H3N2 viruses (HK/8/68 and Ningxia/01/72, also known as Xia-ts) on the NP gene and that of two H1N1 viruses (Tianjin/78/77 and Beijing/1/79) on the M protein gene. By recombination and polyacrylamide electrophoresis migration of the RNA segments of its ts+ recombinant with PR8, the ts lesion of a later H3N2 virus A/Qi/39/79 has now been located on the M protein gene. The possibility for Qi/39/79 of acquiring the M gene lesion by reassortment with concurrently circulating Tianjin/78/77-like (H1N1) virus which also has ts lesion on the M gene was investigated. In contrast to Tianjin/78/77 (H1N1), however, Qi/39/79 complemented well with ts 51, a WSN ts strain with a single M gene lesion. Qi/39/79 and Tianjin/78/77 also complemented each other. Thus, there are two intra-segmental complementation groups of the M gene: Qi/39/79 belongs to one complementation group, while WSN ts 51 and Tianjin/78/77 belong to another. At present, there is no evidence of reassortment involving the genes concerned in the ts lesions of H3N2 and H1N1 viruses under natural conditions.