|MadSci Network: Molecular Biology|
Thanks for your question and your interest. You ask a subtle and interesting question. The simple answer to it is "no". Here are some of the reasons:
Some introns are self splicing. They can splice themselves out without proteins intermediating the process.
In addition, there is more than one complex (set) of proteins and RNAs (called spliceosomes) that splices out introns. If one of the spliceosomes is disabled by a mutation, the other will still be able to splice its target introns.
Another more subtle reason is that most mutations do not cause a complete loss of function in the target protein or RNA. As a member of a multi-protein and RNA complex like the spliceosome, the mutant protein or RNA may still be able to contribute well enough that most (or many) transcripts are still correctly spliced. Even if a certain splicing protein is completely missing, the spliceosome may still function well enough to carry out some splicing, perhaps with a lower efficiency.
For example, in a classic splicing study, mutant U2 snRNAs were tested for their ability to function in splicing and in spliceosome formation. The results indicate that much of the U2 snRNA, including regions essential for detectable binding of the U2-specific proteins A' and B", is dispensable for splicing. In other words, spliceosomes with mutant U2 could still splice transcripts just fine. Here is the article: Cell. 1989 Oct 6;59(1):159-69. Functional analysis of mutant Xenopus U2 snRNAs. Hamm J, Dathan NA, Mattaj IW.
The search "splicing mutant" at www.pubmed.gov turns up 2740 research articles, indicating this is a very interesting and active area of research. You can try the search yourself and look at some of the articles. The articles under the "Review" tab are usually easier to read.
The wikipedia intron article is actually pretty good, and also has references you can follow up on: http://en.wikipedia.org/wiki/Splicing_(genetics)
Take care and enjoy genetics!
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