NONSENSE MUTATIONS INHIBIT RNA SPLICING IN A CELL-FREE SYSTEM - RECOGNITION OF MUTANT CODON IS INDEPENDENT OF PROTEIN-SYNTHESIS

Mutations resulting in premature termination codons reduce the corresp onding mRNA levels. We describe a cell-free system in which depletion of the mutant immunoglobulin kappa mRNA pool correlates with inefficie nt splicing and not with RNA decay. Splicing deficiency does not depen d on the sequence surrounding the in-frame nonsense codon and can be p artially corrected by mutating the methionine initiation codon. Despit e the apparent link between translation and low mutant mRNA levels, in efficient splicing is not dependent on protein synthesis. Abnormal spl icing of mutant immunoglobulin RNA is observed with B-cell but not wit h HeLa or T-cell extracts. A nonsense mutant beta-globin RNA is normal ly spliced by B-cell extract. We propose that the phenomenon exhibits tissue and gene specificity.