Nonfunctional sequences, detection

The molecular defect has recently been linked [7] to a single base substitution, an A—transversion, in the penultimate 3 nucleotide of the third intron of the Apo E gene. This leads to a loss of the correct 3 splice site, thus giving rise to two abnormally spliced mRNA forms. The smaUer form contains 53 nucleotides and the larger one, the entire third intron of the gene. Since both mRNA species contain chain termination codons within the intronic sequence, only short Apo E peptides not detectable by standard gel electrophoretic techniques are produced. Apo E deficiency is, therefore, the result of a molecular error which gives rise to shorter, nonfunctional forms of Apo E. In contrast to Apo B, where the mechanism is posttranslational, here it is clearly pretranslational. 

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