Infectious bronchitis virus: evidence for recombination within the Massachusetts serotype

The spike (S) glycoprotein gene (which encodes two subunits, S1 and S2), the membrane (M) glycoprotein gene and the gene which encodes the products of gene 3 are situated in the infectious bronchitis virus (IBV) genome in the order S1-S2-3-M. The S1 gene of four isolates of the Massachusetts (Mass) serotype, isolated between 1970 and 1984, each differed by only 2 to 3% from that of older Mass serotype isolates, including M41 and H120. Similarly, sequencing of the end of gene 3 and the beginning of the M gene showed that three of the isolates differed from the older Mass isolates by 2% or less. In contrast, the fourth Mass strain, Portugal/322/82, differed by 11% and 24% in gene 3, and the first part of gene M, respectively, suggesting that this strain was a recombinant. It was not possible to identify a putative recombination site but the finding that the S2 gene of Portugal/322/82 differed from other strains much less than did the S1 gene suggests that recombination might have occurred in S2 as a consequence of the high S2 nucleotide homology among IBV strains.