CAMBRIDGE, Mass. - MIT scientists have found a new way that DNA can carry out its work that is about as surprising as discovering that a mold used to cast a metal tool can also serve as a tool itself, with two complementary shapes each showing distinct functional roles.
Professor Manolis Kellis and postdoctoral research fellow Alexander Stark report in the January 1 issue of the journal Genes & Development that in certain DNA sequences, both strands of a DNA segment can perform useful functions, each encoding a distinct molecule that helps control cell functions.
DNA works by complementarity: paired DNA strands serve as a template for each other during DNA replication, and ordinarily only a single DNA strand serves as a template to produce RNA strands, which then go on to produce proteins. The process is similar to the way each bump or dent in a mold is paired with a corresponding dent or bump in the resulting molded object.
While many RNAs are eventually translated into proteins with specific functions, some RNA molecules instead act directly, carrying out roles inside the cell. Certain RNA genes, known as microRNAs, have been shown to play important regulatory roles in the cell, often coordinating important events during the development of the embryo. These microRNAs fold into relatively simple hairpin structures, with two stretches of near-perfect complementary sequence folding back onto each other. One of the two 'arms' of a hairpin is then processed into a mature microRNA.
The surprising discovery is that for some microRNA genes, both DNA strands, instead of just one, encode RNA, and both resulting microRNAs fold into hairpins that are processed into mature microRNAs. In other words, both the tool and its mold appear to be functional. Kellis and Stark found two such microRNA pairs in the fruit fly, and eight more such pairs in the mouse.
The idea that there could be such dual-function strands, where both DN
|Contact: Elizabeth Thomson|
Massachusetts Institute of Technology