Molecular weight determination of the two segments of double-stranded RNA of infectious bursal disease virus, a member of the birnavirus group.

The molecular weights (mol. wts.) of the two double-stranded (ds) RNA segments of infectious bursal disease virus (IBDV) were determined using previously sequenced reovirus genes M3 and S2 as internal ds RNA reference molecules. Electrophoresis under fully denaturing conditions revealed mol. wts. of 2.26 X 10(6) daltons and 1.98 X 10(6) daltons. By direct length measurements under the electron microscope, using two different spreading conditions, the two segments were calculated to be composed of 3274 +/- 79 base pairs (bp) and 2821 +/- 59 bp or 3299 +/- 68 bp and 2830 +/- 73 bp, resulting in mol. wts. of 2.24-2.26 X 10(6) daltons and 1.93-1.94 X 10(6) daltons, respectively. Base pair distances of 2.67 +/- 0.08 A and 2.71 +/- 0.11 A in ds RNA were close to those of the A-RNA form; in ds DNA included as a control, the rise per base pair was 3.18 A, which is consistent with published results. Mol. wts. obtained for IBDV indicate that the RNAs of the other birnaviruses are also smaller than reported.