Mammalian reovirus core protein μ2 initiates at the first start codon and is acetylated

Mammalian reovirus is an enteric virus that contains a double-stranded RNA genome. The genome consists of ten RNA segments that encode eight structural and three non-structural proteins. The structural proteins form a double-layered structure. The innermost layer, called the core, consists of five proteins (lambda1, lambda2, lambda3, mu2, and sigma2). Protein lambda3 is the RNA-dependent RNA polymerase (RdRp) and mu2 is thought to be an RdRp cofactor. Translation of most reovirus proteins is known to commence at the first start codon. However, the translation initiation site of the viral core protein mu2, encoded by the M1 RNA segment, has been in dispute. Although the theoretical molecular weight of mu2 is 83 267 Da the actual molecular weight is unknown because mu2 runs aberrantly in SDS-PAGE and has resisted characterization by Edman degradation, indicating that the amino terminus is post-translationally modified. In this study, we used proteolysis coupled with MALDI-Qq-TOFMS to determine that translation of mu2 initiates at the first AUG codon, that its actual molecular weight approximates the theoretical value of 83 kDa, that the amino terminal methionine residue is removed, and that the next amino acid (alanine) is post-translationally acetylated. Copyright (C) 2002 John Wiley Sons, Ltd.