The late functions of Drosophila sigma virus

Control of sigma virus multiplication by the ref(2)P gene of Drosophila melanogaster: an in vivo study of the PB1 domain of Ref(2)P

Ref(2)P has been described as one of the Drosophila proteins that interacts with the sigma virus cycle. We generated alleles to identify critical residues involved in the restrictive (inhibiting viral multiplication) or permissive (allowing viral multiplication) character of Ref(2)P. We demonstrate that permissive alleles increase the ability of the sigma virus to infect Drosophila when compared to null alleles and we confirm that restrictive alleles decrease this capacity. Moreover, we have created alleles unfunctional in viral cycling while functional for Ref(2)P fly functions. This type of allele had never been observed before and shows that fly- and virus-related activities of Ref(2)P are separable. The viral status of Ref(2)P variants is determined by the amino-terminal PB1 domain polymorphism. In addition, an isolated PB1 domain mimics virus-related functions even if it is similar to a loss of function toward fly-related activities. The evolutionary tree of the Ref(2)P PB1 domain that we could build on the basis of the natural allele sequences is in agreement with an evolution of PB1 domain due to successive transient selection waves.

[A genetic study of the interaction of Piry virus with drosophila]

Piry virus mutants selected for altered growth properties in Drosophila melanogaster have previously been designated agD mutants. This paper presents a classification scheme for grouping some of these mutants and also presents the characteristics of some members of each group. Analysis, for each agD clone, of the mean incubation time at 20 degrees C relative to the mean incubation time at 28 degrees C (t20,t28), compared to the range of similar data for wild-type virus enabled us to define 4 classes of agD mutant: (1) mutants equally affected at both temperatures, (2) cold-sensitive mutants in drosophila (csD), (3) heat-sensitive mutants in drosophila (tsD) and (4) mutants whose mean incubation time could not be estimated at either 20 or 28 degrees C. All agD mutants are listed. The majority of them were also ts in chicken embryo cells (CEC), and some were classified into complementation groups. Some correlations were noted. For example, the agD mutants that were ts+ in CEC were frequently (7 out of 12) weakly cold-sensitive in drosophila. Those tsD mutants which were also ts in CEC, all belonged to complementation group I (L protein). True csD mutants, whose divergence of incubation time with wt regularly increased, and which were also ts in CEC, all belonged to group I except for one which belonged to group V (G protein). Three mutants fell into a distinct sub-class of csD mutants, characterized by a defect in the CO2 sensitivity symptom expression below a definite temperature. One of these which was further characterized was shown to be in complementation group V. Some mutants of the fourth class were examined for their fly-invading capacity. This was found to be more-or-less strongly affected. Among these mutants, independent of this phenomenon, mutations were assigned to L, N and G proteins, suggesting that different physiological defects are involved. A comparison was made of the phenotypes in drosophila of some of the agD mutants with other members of the vesiculovirus family. The analogy of sigma rhabdovirus with tsD mutants is also reported.