Study of Non protein-Coding DNA and Regulatory Function
By over the books and Internet we try to learn about Non protein-Coding DNA and Regulatory Function . As more genomes are sequenced, we learn that much of the genome is composed of non-coding DNA. The repetitive DNA is often retrotransposon DNA, contributing to as much as 30% of animal genomes and 40-80% of plant genomes. Perhaps the most unexpected finding in comparing the mouse and human genomes lies in the similarities between the repetitive DNA, mostly retrotransposons, in the two species. This DNA does not code for proteins. A survey of the location of retrotransposon DNA in both species shows that it has independently ended up in comparable regions of the genome. At first glance it appeared that all this extra DNA was "junk" DNA, DNA just along for the ride. But it is beginning to look like this non protein-coding DNA may have more of a function than was previously assumed. The possibility that this DNA is rich in regulatory RNA sequences, such as those described in chapter 18, is being actively investigated. RNAs that are not translated can play several roles, including silencing other genes. Small RNAs can form double-stranded RNA complementary mRNA sequences, blocking translation. T can also participate in the targeted degradation of RNAs.
In one study, researchers collected almost all of the transcripts made by mouse cells taken from every tissue. though most of the transcripts coded for mouse proteins many as 4280 could not be matched to any known mouse protein. This finding suggests that a large part of the transcribed genome consists of genes that do not code for proteins-- is, transcripts that function as RNA. Perhaps this function explain why a single retrotransposon can cause heritable differences in coat color in mice.
DNA that does not code for protein may regulate gene expression, often through its RNA transcript. Nonprotein-coding sequences can be found in retrotransposon-rich regions of the genome.
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