Characterization of temperature-sensitive mutants of measles virus

Ten temperature-sensitive (ts) mutants derived from the Edmonston strain of measles virus were characterized by the complementation test and were shown to have four defective sites (A, B, C, and D). Five ts mutants which were confirmed to have a defective site D, induced neither cytopathic effect (CPE) nor an infectious virus. Among the other five ts mutants which produced viral proteins with CPE and showed positive HAD at 39.5 degrees C, the three ts mutants (P253-505, P333, and F2-104) were studied in detail. P253-505 had a defective site C and both P333 and F2-104 had a defective site A. P253-505 and F2-104 produced neither a cell-free nor cell-associated infectious virus and P333 produced only a low level of cell-associated infectious virus. P253-505 and P333 produced virus particles at 39.5 degrees C, while F2-104 did not. The pulse-chase experiment showed a normal pattern of synthesis and processing of viral proteins, but immunofluorescence tests using monoclonal antibodies indicated that P253-505 lacked two epitopes of the M protein at 39.5 degrees C, and both P333 and F2-104 lacked one epitope of the P protein. The lack of these viral epitopes was shown to correlate with the temperature-sensitivity of the three ts mutants.