tokens: These results indicate the usefulness of cycloheximide treatment in evaluating the abnormal processing of mRNA due to splice - site mutations , because ( i ) aberrant splicing often generates a premature termination codon , ( ii ) transcripts with premature termination codons can occur at low or undetectable levels due to nonsense - mediated mRNA decay , and ( iii ) the levels of these transcripts can be increased by cycloheximide .