CORE PROTEIN MU-2 IS A 2ND DETERMINANT OF NUCLEOSIDE TRIPHOSPHATASE ACTIVITIES BY REOVIRUS CORES

NTPase activities in mammalian reovirus cores were examined under vari ous conditions that permitted several new differences to be identified between strains type 1 Lang (T1L) and type 3 Dearing (T3D). One diffe rence concerned the ratio (at pH 8.5) of ATP hydrolysis at 50 degrees C to that at 35 degrees C. A genetic analysis using T1L x T3D reassort ant viruses implicated the L3 and M1 gene segments in this difference, with M1 influencing ATPase activity most strongly at high temperature s. L3 and M1 encode the core proteins lambda 1 and mu 2, respectively. Another difference concerned the absolute levels of GTP hydrolysis by cores at 45 degrees C and pH 6.5. A genetic analysis using T1L x T3D reassortants implicated the M1 gene as the sole determinant of this di fference. The results of these experiments, coupled with previous find ings (S. Noble and M. L. Nibert, J. Virol. 71:2182-2191, 1997), sugges t either that a single type of NTPase in cores is strongly influenced by two different core proteins-lambda 1 and mu 2-or that cores contain two different types of NTPase influenced by the two proteins. The fin dings appear relevant for understanding the complex functions of reovi rus cores in RNA synthesis and capping.