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The ref(2)P gene of Drosophila melanogaster is implicated in sigma rhabdovirus multiplication. A permissive allele was cloned and sequenced. The structural gene (3.1 kbp) is divided into three exons. The mRNAs are heterogeneous in size. They differ only in the 5′ end of the first exon. The sequence upstream of the short mRNAs contains classical promoter elements. No TATA and CAAT boxes are appropriately positioned upstream of the initiation sites of the long mRNAs, but several repeats, palindromic sequences and inverted CAAT boxes are present. These observations, together with the tissue‐dependent distribution of short and long transcripts, support the hypothesis of the existence of at least two classes of genuine initiation sites. The long size of the untranslated leader RNA region suggests a control of gene expression at the translation level. The same translation product of 599 amino acids (76.3 kd) is predicted for all mRNAs, but the in vitro translation product migrates in SDS‐PAGE with a higher apparent mol. wt (115‐125 kd). The putative ref(2)P protein contains internal repeats, PEST regions which may be signals for protein degradation, and interesting structural motifs such as zinc finger and amphiphilic helices. These later motifs could be mitochondrial pre‐sequences. The degeneration of mitochondria is observed in the spermatids of sterile male flies homozygous for the loss‐of‐function alleles. The amino acid sequence of the ref(2)P product shows no homology with any known protein from the data banks.

The genome of the sigma rhabdovirus of Drosophilamelanogaster consists of six genes in the order 3′ N-2-3-4-G-L 5′. The nucleotide sequences of the N and of the fourth genes were determined from cDNA clones. Each gene contained a single long open reading frame encoding polypeptides with predicted MW of 50 and 25 kDa, respectively. Evidence that these genes encode the nucleocapsid N and the matrix M proteins were obtained using antibodies raised against recombinant proteins derived from the cloned genes and expressed in Escherichia coli.The M and N predicted amino acid sequences were compared with those of other rhabdoviruses. The M protein of sigma virus shared a similar domain arrangement to the other M proteins, but it showed very little sequence conservation. The N protein of sigma virus showed no significant hemology with its counterpart in SYNV or IHNV and VSHV; it did, however, show sequence homology with the N of four vesiculoviruses and two lyssaviruses. The extent of amino acid identity suggests that sigma virus occupies an intermediate evolutionary position between these two genera. Some conserved motifs in the M and N proteins were deduced from the comparisons.

Expression of the src gene of Rous sarcoma virus in chicken embryo neuroretinal cells results in morphological transformation and sustained proliferation of this normally resting cell population. PA101 and PA104 are two mutants of Rous sarcoma virus which induce neuroretinal cell proliferation in the absence of morphological transformation. Their mitogenic property is temperature sensitive, and they both encode p60src proteins with low kinase activity. To study the role of the mitogenic function and protein kinase activity of p60src in tumorigenesis, we investigated the oncogenicity of PA101 and PA104. Both mutants were less tumorigenic than wild-type virus when injected into chicks. Tumorigenicity was further assayed by inoculating infected chicken embryo fibroblasts and neuroretinal cells onto the chorioallantoid membrane of embryonated duck eggs. This system provides a nonpermissive and immunodeficient environment for xenogenic cell grafting and allows the study of cell tumorigenicity within a temperature range of 37 to 39.5 degrees C. Chicken embryo fibroblasts and neuroretinal cells infected with PA101 were as tumorigenic as wild type-infected cells at 37 degrees C, but tumor development was significantly reduced at 39.5 degrees C. In contrast, both cell types infected with PA104 displayed sharply reduced tumorigenicity. Cell cultures derived from PA101 tumors induced on the chorioallantoid membrane were similar to the corresponding cells maintained in vitro in terms of morphology, production of plasminogen activator, relative amounts of phosphotyrosine in total cellular proteins, and phosphorylation of 34,000-molecular-weight protein. These results indicate that the expression of the mitogenic function of src does not account per se for cell tumorigenicity and that tumor formation is compatible with low levels of p60src protein kinase activity.

In cultured Drosophila melanogaster cells, vesicular stomatitis virus (VSV) established a persistent, noncytopathic infection. No inhibition of host protein synthesis occurred even though all cells were initially infected. No defective interfering particles were detected, which would explain the establishment of the carrier state. In studies of the time course of viral protein synthesis in Drosophila cells, N, NS, and M viral polypeptides were readily detected within 1 h of infection. The yield of G protein and one of its precursors; G1, was very low at any time of the virus cycle; the released viruses always contained four to five times less G than those produced by chicken embryo cells, whatever the VSV strain or serotype used for infection and whatever the Drosophila cell line used as host. Actinomycin D added to the cells before infection enhanced VSV growth up to eight times. G and G1 synthesis increased much more than that of the other viral proteins when the cells were pretreated with the drug; nevertheless, the released viruses exhibited the same deficiency in G protein as the VSV released from untreated cells. Host cell control on both G-protein maturation process and synthesis at traduction level is discussed in relation to G biological properties.