Role of the Drosophila genome in sigma virus multiplication II. Host spectrum variants among the haP mutants

Abstract Five Drosophila genes are known which act specifically on the multiplication of the Sigma virus: ref(1)H , ref(2)M , ref(2)P , ref(3)O , and ref(3)D . Alleles M m , P p , and D p of ref(2)M , ref(2)P , and ref(3)D genes, respectively, decrease the probability of initiating infection by Sigma virus 23. Allele O e of ref(3)O increases the mean incubation time required at 20° for the expression of C0 2 sensitivity, the symptom of Sigma infection in Drosophila . The known alleles of ref(1)H are permissive for virus 23. haP mutants (mutants adapted to ref(2)P p ) have been selected from virus 23. Among the haP mutants, the frequency of viruses more adapted or more restricted in M m flies is about 0.5 and is clearly higher than among viruses not screened for P p adaptation. Among the haP mutants, we also observe viruses more restricted by D p and O e alleles. Certain haP mutants are also restricted by H h and 0 o alleles, which are permissive alleles for virus 23. The frequency of the variations for the alleles D p O e , H h , and 0 o is about 0.1, which is high compared to the frequency of haP mutants after mutagenesis (about 5 × 10 −3 ). These observations suggest the hypothesis that a mutation affecting the viral protein-genome complex, for instance affecting early viral functions as the haP 7, 21, 22, 23, and 29 mutations, may modify viral interactions with the H , M , P , 0, and D host genes.