A Comparison of Molecular Weights of Foot-and-Mouth Disease Virus RNA Fragments Determined from Lengths and s-Rates

A comparison was made of the calculated mol. wt. of RNA fragments from foot-and-mouth disease virus (FMDV) types A12 strain 119, C3 Resende and O1 Brugge. The mol. wt. were calculated by two methods: from the measurements of strand lengths in the electron micrographs and from the observed sedimentation rates (s-rates). RNA extracted from virus by dialysis against water usually had three to four prominent strands of different lengths. Mol. wt. calculated from s-rates (and converted to strand lengths) generally agreed with those measured on electron micrographs. Differences which occurred appeared to be attributable to further breakage during processing for electron microscopy. Major fragment strand lengths range from 0-65 to 2-45 mum. The modal lengths of RNA fragments were preparation-dependent, ranging from 1-25 to 1-95 mum for A12 119, 1-05 to 1-75 mum for C3 Resende, and 1-65 to 2-45 mum for O1 Brugge. There was one fragment length 1-95 mum common to all three types of FMDV RNA and several others which appear in at least two types. Calculations using the molar ratios of nucleotide residues in FMDV RNA, a mol. wt. of FMDV RNA of 2-65 X 10(6) and an internucleotide spacing of 3-17 A indicate that intact FMDV RNA should be 2-62 mum long and therefore would contain approx. 8270 nucleotides. The derived mathematical expression for the relationship between mol. wt. (M) and s-rate (S) giving the best fit for all data was M = 1725 S2-07, a result close to that derived by Spirin (1963) for other single-stranded RNAs.