It appears that different members of the Cystoviridae use different host proteins to activate or to regulate transcription [4]. The control of transcription in Φ2954 involves the nature of the first base of the segment L transcript while that of Φ6 and its close relatives involves 10058-F4 the nature of the second base. Results and Discussion Twenty five new isolates of members of the Cystoviridae were obtained from the leaves of radish, carrot and onion plants. Five of the isolates showed similarity

to previously isolated Φ12 [5] although their host ranges differed from that of Φ12. Radish leaves were incubated with LB broth. The liquid was mixed with a culture of Pseudomonas syringae LM2489 which is a rough LPS derivative of the original host strain for the cystoviruses [2]. Plaques were tested for sensitivity to chloroform. An isolate named Φ2954 was

found to contain three segments of dsRNA. The sizes of the RNA segments differed from those of the known cystoviruses. The host range of the phage was similar to that of Φ6 in that it did not propagate on strains missing type IV pili but did propagate on strain HB10Y which has type IV pili and smooth LPS. Phage was purified by sedimentation and equilibrium banding in sucrose or Renocal (Bracco Diagnostics) gradients. Purified phage was analyzed by polyacrylamide gel electrophoresis (Fig. 1). The migration of the proteins SIS3 molecular weight was similar to that seen for most of the Cystoviridae and that of protein P8 was similar to that of Φ12 in that it appeared to have a molecular weight of 22 kd rather than that of 16 kd shown by most of the Cystoviridae. cDNA was prepared from the genomic dsRNA of the phage or from transcripts produced in vitro by nucleocapsids of the virus. cDNA was prepared using random hexamers or polyA tailing in conjunction with oligodT PF-6463922 ic50 priming. The sequences

were compiled into the maps shown in Figure 2. The sizes of the genomic segments were found to be 2578 bp, 3606 bp and 6501 bp respectively for segments S, M and L. Blast searches Tacrolimus (FK506) showed no significant nucleotide similarity with other phages but searches of amino acid sequence showed significant similarity to many of the gene products of bacteriophage Φ12 (Table 1) [6]. In particular, the amino acid sequence of the viral RNA polymerase, P2, was closely related to that of Φ12. Several of the differences shown by Φ12 relative to Φ6 were present in P2 of Φ2954. This was true of the regions in P2 of Φ6 at nucleotide positions K223 and R225; R268 and R 270; and S452 that deal with triphosphate binding and catalytic sites [7]. Moreover, the 5′ terminal sequences of the segment transcripts resembled, but were not identical to those of the Φ12 genomic segments (Fig. 3). Φ12 differs from other members of the Cystoviridae in the base sequences at the 5′ termini of plus strand copies of the genome.