Mutation in an intervening sequence splice junction in man

Duplication followed by deletion accounts for the structure of an Indian deletion beta (0)-thalassemia gene

Nucleotide sequence analysis of a cloned deletion beta-globin gene from a patient with beta(0)-thalassemia demonstrates a 619 nucleotide deletion extending from the 3' third of the second intervening sequence through 209 bases of 3' flanking DNA. However, an additional novel heptanucleotide was identified between the deletion endpoints, suggesting a complex etiology for this rearrangement.

Deletions at intervening sequence splice sites in the alcohol dehydrogenase gene of Drosophila

Two formaldehyde-induced, homozygous viable ADH-negative mutants, Adhfn4 and Adhfn6, possess no material that cross-reacts with antibody directed against ADH, no mature mRNA of wild-type size, and greatly reduced amounts of RNA that hybridizes with an Adh probe. We have cloned the genomic DNA sequences from these mutants in bacteriophage lambda Charon 4 and subcloned the Adh region into plasmid vector pBR327. Restriction analyses revealed one small deletion in each of these mutants and DNA sequencing showed that the splice junctions of the 65-base pair (bp) intervening sequence (IVS) were altered. Both cloned mutant Adh genes, as well as the wild-type gene, are capable of promoting correct specific transcription initiation in HeLa cell nuclear extracts in vitro. We conclude that Adhfn4 and Adhfn6 are defective in RNA processing. Our results provide evidence for the importance of the splice junction sequences in normal ADH RNA processing and stabilization in Drosophila. We also speculate that splicing of ADH RNA proceeds in a nonrandom manner: mutations in one of the intervening sequences appear to cause accumulation of a large ADH RNA containing at least one other IVS.

Genetic diseases: diagnosis by restriction endonuclease analysis

We have summarized a number of different genetic disorders which can be diagnosed at the DNA level using restriction endonuclease fragment analysis. A whole spectrum of defects can be recognized: point mutations, deletions, additions, and crossing-over products or hybrid genes. These same restriction endonuclease techniques can enable different genes to be marked by polymorphism patterns. Thus, abnormal genes can be identified even if their exact DNA lesion is unknown or cannot be directly detected. The progress that has been made with the hemoglobinopathies and the experience from this group of single gene disorders should find application to other diseases as soon as specific probes become available.

Construction of a yeast actin gene intron deletion mutant that is defective in splicing and leads to the accumulation of precursor RNA in transformed yeast cells

The actin gene in yeast Saccharomyces cerevisiae is interrupted by a 309-base-pair intron within the protein-coding region. By using nuclease BAL-31, several intron deletion mutants were constructed to define sequences at the 5' splice junction that are required for RNA splicing. Extensive parts of the intron can be removed without affecting correct splicing. One mutant gene from which the invariant thymidine residue in the second intron position was deleted led to the accumulation of large amounts of unspliced actin mRNA when introduced into yeast cells through a recombinant high-copy-number plasmid. No evidence for the usage of alternative splice sites was obtained.