- Volume 53, Issue 1, 1981

S-Adenosyl-l-methionine (SAM), a methyl donor, and its analogue S-adenosyl-l-homocysteine (SAH), an inhibitor of methylation, stimulate the activity of spring viraemia of carp virus (SVCV) virion transcriptase. The stimulation observed for SVCV is analogous to that observed previously (Furuichi, 1974, 1978) for a totally unrelated virus, cytoplasmic polyhedrosis virus (CPV). In the absence of exogenous SAM, RNA with 5′-methylated termini (presumptive GpppAmpAp) was produced, indicating that SVCV has an endogenous methyl donor. Significantly less methylated termini were produced when SVCV nucleocapsids were used to prime in vitro transcription reactions, suggesting that the majority of the endogenous methyl donor is not associated with the nucleocapsid. Partial removal of endogenous methyl donor by preparing nucleocapsids did not have any effect on the degree of stimulation by exogenous SAM or SAH. We conclude from this study that SAH has two effects on SVCV transcription, inhibition of methylation and stimulation of transcription.

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 and 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 at 53S (T), 99S (M) and 120S (B).

At equilibrium in CsCl 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 five additional nucleoproteins (S1 to S5). 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 each of RNA-2 and RNA-1, components S1 to S4 contain one, two, four and five molecules of satellite RNA-3 respectively. Component S5 differs from the others in that it may contain one molecule each of RNA-2 and RNA-3. MyLRV and TBRV-S were serologically unrelated. Based on the size of RNA-2, MyLRV appears to be closer to CLRV than to TBRV.