Printed in Great Britain 57 A Comparison of Myrobalan Latent Ringspot Virus with Other

The type strain of myrobalan latent ringspot virus (MyLRV) and the beet ringspot strain of tomato black ring virus (TBRV-S) were compared with respect to some of their physicochemical nd serological properties. A strain of MyLRV without satellite RNA [MyLRV(--3)] and a strain of cherry leafroll virus (CLRV) were also used for comparison purposes. In sucrose density gradients and in the analytical ultracentrifuge, MyLRV and MyLRV(-3) sedimented as three components, T M and B, with sedimentation coefficients of 50S, 109S and 125S respectively. TBRV-S also had three components sedimenting at53S (T), 99S (M) and 120S (B). At equilibrium in CsCI only two components were resolved for TBRV-S with buoyant densities of 1-44 g/ml (M) and 1.50 g/ml (B), whereas MyLRV(-3) yielded three components with the buoyant densities of 1.28 g/ml (T), 1.47 g/ml (M) and 1.51 g/ml (B). MyLRV preparations contained fiv additional nucleoproteins (S1 to $5). A study of the distribution of RNAs in the centrifugal components of MyLRV and MyLRV(--3), based on differences in buoyant densities and RNA recovery from different nucleoproteins, suggests that whereas M and B fractions contain one molecule ach of RNA-2 and RNA-1, components S t to S 4 contain one, two, four and five molecules of satellite RNA-3 respectively. Component S 5 differs from the others in that it may contain one molecule ach of RNA-2 and RNA-3. MyLRV and TBRV-S were serologically unrelated. Based on th size of RNA-2, MyLRV appears to be closer to CLRV than to TBRV