Translation and M1 double-stranded RNA propagation: MAK18 = RPL41B and cycloheximide curing.

MAK18 is one of nearly 30 chromosomal genes of Saccharomyces cerevisiae necessary for propagation of the killer toxin-encoding M1 double-stranded RNA satellite of the L-A double-stranded RNA virus. We have cloned and sequenced MAK18 and find that it is identical to RPL41B, one of the two genes encoding large ribosomal subunit protein L41. The mak18-1 mutant is deficient in 60S subunits, which we suggest results in a preferential decrease in translation of viral poly(A)-deficient mRNA. We have reexamined the curing of M1 by low concentrations of cycloheximide (G. R. Fink and C. A. Styles, Proc. Natl. Acad. Sci. USA 69:2846-2849, 1972), which is known to act on ribosomal large subunit protein L29. We find that when M1 is supported by L-A proteins made from the poly(A)+ mRNA of a cDNA clone of L-A, cycloheximide does not decrease the M1 copy number, consistent with our hypothesis.