Effects of length and mRNA secondary structure on the interaction of bovine mitochondrial ribosomes with messenger RNA.

The mRNA for cytochrome oxidase subunit II (CoII) from bovine mitochondria binds to the small subunit of the mitochondrial ribosome in the absence of auxiliary factors. The synthetic polymer poly(U) is effective in competing with CoII mRNA for binding, although the polymer poly(A,U,G) competes very weakly. The effects of mRNA length on the interaction between the 28 S ribosomal subunit and mRNA have been examined using truncated derivatives of CoII mRNA. These results indicate that there is a minimum length of approximately 400 nucleotides required for the efficient binding of the mRNA to the small subunit. Shorter mRNAs will bind, but do so with much lower association constants. mRNAs of various lengths but with reduced secondary structure were prepared by substituting ITP for GTP during in vitro transcription reactions. These derivatives show the same effects of length as do the normal mRNA, indicating that RNA secondary structure is not a critical factor in subunit-mRNA interaction. The binding of the mRNA to the 28 S subunit is not influenced by the presence of guanine nucleotides or by the presence of a triphosphate at the 5' end of the RNA.