ASU Research E-Magazine: Translating DNA

Robert Blankenship uses techniques similar to those used by scholars who study ancient manuscripts such as the Bible or The Iliad. The objects of his analysis are not writings, however, they are tiny twisted bits of protein. The ASU chemist searches for evolutionary relationships among the proteins.

Imagine, if you will, a manuscript written 3,000 years ago. The original manuscript does not exist, only copies. In ancient times, the only way to make a copy was for someone trained in reading and writing, perhaps a monk, to painstakingly transcribe the information, letter by letter.

Often, these human copiers were trained to copy but not to understand, much like a Xerox machine or the cellular machinery which duplicates DNA. If one letter were substituted for another, it might not be noticed, but that mistake would likely be preserved on subsequent duplications.

Clues as to what the original text looked like can be gleaned from the study of copies and the differences between them. Note the following three sentences:

Sentence 1:
The great white lion ate the angry man.

Sentence 2:
The great golden lion ate the hapless man.

Sentence 3:
The great white lion smote the hapless man.

By choosing the most common words in the sentences, one can construct a hypothetical ancestor sentence, like this:

New Sentence:
The great white lion ate the hapless man.

The same follows for copies of genetic material. Imagine three sequences of RNA coding for amino acids that are similar to each other. Parts of them share sequences, as follows:

Sequence 1:
A U G U U U C C U A C A G C A

Sequence 2:
A U G U C U C C U A A A G C A

Sequence 3:
A U G U U U C C C A A A G C A

One can build a sequence that combines features that are most common:

New Sequence:
A U G U U U C C U A A A G C A

It is likely that the ancient original sequence looked more like the newly generated sequence than any of the existing modern sequences.

Blankenship and his students use powerful computers to analyze significant chunks of the genetic material in the various photosystems now flourishing in plants. One section they study is called the heterodimeric complex.

“The heterodimeric complex undoubtedly occurred by having a single gene that duplicated and then diverged to form a pair,” Blankenship explains. “This is what happens in Photosystem I, Photosystem II, in purple bacteria, and so on. And it’s clear that this happened at least three different times, because the two halves of the complex are more similar to each other than they are to another complex.”

For example, in Photosystem I, the two parts of the heterodimeric complex are very similar to each other. They are about 50 percent identical. But they are only about 10 or 20 percent identical to the complex in Photosystem II.

“The two halves of the Photosystem II complex are about 30 percent identical to each other,” he continues. “What happened? We think that this gene duplication and divergence happened at least three or four different times to form these separate classes of reaction centers.”—John Svetlik