Our major project deals with the replication of 06, a virus containing three segments of double-stranded RNA, an internal RNA polymerizing activity, and a lipoprotein coat. 06 infects Pseudomonas phaseolicola, a plant pathogen. We have isolated several hundred temperature-sensitive mutants of 06 and assigned them, by complementation-recombination spot tests, to three groups corresponding the three RNA segments. These ts mutants are being further assigned to genes by complementation with nonsense mutants provided by L. Mindich. Emphasis in the near future will be on characterization of wild type and mutant RNA polymerizing activities and studies of viral RNA replication and packaging. BIBLIOGRAPHIC REFERENCES: Britton, J.R. and Haselkorn, R. Macromolecular synthesis in T7 infected F' cells. Virology 67, 264-275 (l975). Kells, S.S., Ohtsuki, M. and Haselkorn, R. The structure of bacteriophage T4 Gene 12 protein. J. Mol. Biol. 99, 349-351 (l975).